1. |
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2. |
- Abb, Marcel J.S., et al.
(författare)
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Thermal Stability of Single-Crystalline IrO2(110) Layers : Spectroscopic and Adsorption Studies
- 2020
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:28, s. 15324-15336
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of ultrathin single-crystalline IrO2(110) films with the gas phase proceeds via the coordinatively unsaturated sites (cus), in particular Ircus, the undercoordinated oxygen species on-top O (Oot) that are coordinated to Ircus, and bridging O (Obr). With the combination of different experimental techniques, such as thermal desorption spectroscopy, scanning tunneling microscopy (STM), high-resolution core-level spectroscopy (HRCLS), infrared spectroscopy, and first-principles studies employing density functional theory calculations, we are able to elucidate surface properties of single-crystalline IrO2(110). We provide spectroscopic fingerprints of the active surface sites of IrO2(110). The freshly prepared IrO2(110) surface is virtually inactive toward gas-phase molecules. The IrO2(110) surface needs to be activated by annealing to 500-600 K under ultrahigh vacuum (UHV) conditions. In the activation step, Ircus sites are liberated from on-top oxygen (Oot) and monoatomic Ir metal islands are formed on the surface, leading to the formation of a bifunctional model catalyst. Vacant Ircus sites of IrO2(110) allow for strong interaction and accommodation of molecules from the gas phase. For instance, CO can adsorb atop on Ircus and water forms a strongly bound water layer on the activated IrO2(110) surface. Single-crystalline IrO2(110) is thermally not very stable although chemically stable. Chemical reduction of IrO2(110) by extensive CO exposure at 473 K is not observed, which is in contrast to the prototypical RuO2(110) system.
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3. |
- Abbas, Zareen, 1962, et al.
(författare)
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Size-Dependent Surface Charging of Nanoparticles
- 2008
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Ingår i: J of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5715-5723
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Tidskriftsartikel (refereegranskat)abstract
- Experimental interest in the possible curvature dependence of particle charging in electrolyte solutions is subjected to theoretical analysis. The corrected Debye-Hückel theory of surface complexation (CDH-SC) and Monte Carlo (MC) simulation are applied to investigate the dependence of surface charging of metal oxide nanoparticles on their size. Surface charge density versus pH curves for spherical metal oxide nanoparticles in the size range of 1-100 nm are calculated at various concentrations of a background electrolyte. The surface charge density of a nanoparticle is found to be highly size-dependent. As the particle diameter drops to below 10 nm there is considerable increase in the surface charge density as compared with the limiting values seen for particles larger than 20 nm. This increase in the surface charge density is due to the enhanced screening efficiency of the electrolyte solution around small nanoparticles, which is most prominent for particles of diameters less than 5 nm. For example, the surface charge densities calculated for 2 nm particles at 0.1 M concentration are very close to the values obtained for 100 nm particles at 1 M concentration. These predictions of the dependence of surface charge density on particle size by the CDH-SC theory are in very good agreement with the corresponding results obtained by the MC simulations. A shift in the pH value of the point of zero charge toward higher pH values is also seen with a decreasing particle size.
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4. |
- Abid, Jean-Pierre, et al.
(författare)
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Controlled reversible adsorption of core : Shell metallic nanoparticles at the polarized water/1,2-dichloroethane interface investigated by optical second-harmonic generation
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:25, s. 8849-8855
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Tidskriftsartikel (refereegranskat)abstract
- We report the observation of the reversible adsorption of core-shell gold-silver nanoparticles at the polarized water/1,2-dichloroethane interface using the nonlinear optical technique of surface second-harmonic generation. This study unambiguously demonstrates the excellent stability against aggregation of these core-shell nanoparticles, namely, gold core nanoparticles coated with silver layers of variable thickness, in the presence of an electrolyte salt like lithium chloride. Furthermore, it is also demonstrated that the adsorption of the nanoparticles is reversible by modulating the applied potential at water/1,2-dichloroethane interface. The analysis of these results is performed within the Debye-Huckel approximation of the electrostatic interactions between the nanoparticles. This approach shows that the stability of core-shell nanoparticles can be attributed to the formation of a silver oxide layer at the Surface of the particles.
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5. |
- Abou-Hamad, Edy, et al.
(författare)
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Hydrogenation of C-60 in Peapods: Physical Chemistry in Nano Vessels
- 2009
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Ingår i: The Journal of Physical Chemistry C. - WASHINGTON, DC 20036 : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 113:20, s. 8583-8587
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenation of C-60 molecules inside SWNT was achieved by direct reaction with hydrogen gas at elevated pressure and temperature. Evidence for the C-60 hydrogenation in peapods is provided by isotopic engineering with specific enrichment of encapsulated species and high resolution C-13 and H-1 NMR spectroscopy with the observation of characteristic diamagnetic and paramagnetic shifts of the NMR lines and the appearance of sp(3) carbon resonances. We estimate that approximately 78% of the C-60 molecules inside SWNTs are hydrogenated to an average degree of 14 hydrogen atoms per C-60 molecule. As a consequence, the rotational dynamics of the encapsulated C60Hx molecules is clearly hindered. Our successful hydrogenation experiments open completely new roads to understand and control confined chemical reactions at the nano scale
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6. |
- Abrahamsson, Brita, 1989, et al.
(författare)
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NOx Adsorption on ATiO(3)(001) Perovskite Surfaces
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:32, s. 18495-18503
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory calculations have been used to explore NO adsorption on perovskite oxides surfaces ATiO(3)(001) with A = Ca, Sr, Ba. NO adsorbs weakly on all facets with no apparent A-ion dependence, whereas NO2 adsorbs preferably over AO-terminated surfaces with adsorption energies that correlate with the ionization potentials of the alkaline earth atoms. Simultaneous adsorption of NO and NO2 is found to substantially enhance the stability of the adsorbates owing to an oxide mediated electron-pairing mechanism. Stabilization is also predicted for NO/O-2 adsorption, and it is suggested that the presence of oxygen favors the formation of nitrite/nitrate pairs. It is found that the NOx adsorption properties can be modified by mixing alkaline earth cations in the perovskite framework. The results are put in context by comparison with NOx adsorption on the corresponding (001) facets of alkaline earth metal oxides and TiO2(110).
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7. |
- Agarwal, Nisha Rani, 1987, et al.
(författare)
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Nonlinear Optical Properties of Polyynes: An Experimental Prediction for Carbyne
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:20, s. 11131-11139
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Tidskriftsartikel (refereegranskat)abstract
- We present the experimental determination of the vibrational contribution to molecular second hyperpolarizability (gamma(vib)) of very long polyynes that have been recently made available thanks to progress in chemical synthesis. Based on a simple theoretical model, the available experimental data allow estimating the asymptotic behavior of the vibrational contribution to molecular hyperpolarizability for increasing chain length.
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8. |
- Agrios, Alexander G., et al.
(författare)
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Low-temperature TiO2 Films for Dye-sensitized Solar Cells : Factors Affecting Energy Conversion Efficiency
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:27, s. 10021-10026
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor films prepd. by electrostatic layer-by-layer deposition can be used to fabricate dye-sensitized solar cells after low-temp. treatment (150 DegC). However, the resulting photocurrent is much less than when the film is sintered at 500 DegC. The difference in short-circuit current is a factor of 2.2 with the Ru-based dye N719 and is 3.5 with the org. dye D5. The photocurrent at a given wavelength is proportional to the light-harvesting efficiency, charge injection effciency, and charge collection efficiency. Sintered films take up more than 60% more of either dye than unsintered films and therefore absorb more photons. Electron injection is hindered in unsintered films due to a conduction band edge potential 100 mV more neg. than in a sintered electrode. Addnl. injection effects could be due to adsorption of the dye to polymer rather than to TiO2 in unsintered films, although our measurements were inconclusive on this point. Kinetic studies show electron transport times (ttr) an order of magnitude faster then electron lifetimes (te) in both sintered and unsintered electrodes. Furthermore, a Li+ insertion expt. shows that both films have good elec. connectivity between TiO2 nanoparticles. Unsintered films thus exhibit efficient charge transport despite the presence of polymer and the lack of heat treatment to induce necking.
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9. |
- Aharony, A., et al.
(författare)
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Effects of Different Lead Magnetizations on the Datta-Das Spin Field-Effect Transistor
- 2019
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:17, s. 11094-11100
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Tidskriftsartikel (refereegranskat)abstract
- A Datta-Das spin field-effect transistor is built of a one-dimensional weak link, with Rashba spin-orbit interactions (SOIs), which connects two magnetized reservoirs. The particle and spin currents between the two reservoirs are calculated to lowest order in the tunneling through the weak link and in the wide-band approximation, with emphasis on their dependence on the origins of the "bare" magnetizations in the reservoirs. The SOI is found to generate magnetization components in each reservoir, which rotate in the plane of the electric field (generating the SOI) and the weak link, only if the "bare" magnetization of the other reservoir has a nonzero component in that plane. The SOI affects the charge current only if both reservoirs are polarized. The charge current is conserved, but the transverse rotating magnetization current is not conserved because the SOI in the weak link generates extra spin polarizations which are injected into the reservoirs.
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10. |
- Ahlund, John, et al.
(författare)
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Molecular growth determined by surface domain patterns
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:17, s. 6887-6890
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Tidskriftsartikel (refereegranskat)abstract
- The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.
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11. |
- Ahmad, Y., et al.
(författare)
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NMR and NEXAFS Study of Various Graphite Fluorides
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:26, s. 13564-13572
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Tidskriftsartikel (refereegranskat)abstract
- Graphite fluorides with different structural types (CyF)(n) (y = 2.5, 2, and 1) and room temperature graphite fluorides were studied by solid state,NMR and NEXAFS. Data extracted from those two techniques are complementary, providing information about the C-F bonding and the hybridization character of the carbon atom valence states. The comparison of data obtained by different methods such as NMR, Raman, and X-ray absorption leads to similar conclusions regarding the chemical bonding in fluorographites. Several major configurations of fluorinated graphites are discussed, that is, planar sheets with mainly sp(2) hybridization in room temperature graphite fluorides and corrugated sheets with sp(3) hybridization in covalent high temperature graphite fluoride. Different references such as highly oriented pyrolytic graphite (HOPG), graphitized carbon nanodiscs (graph-CNDs) and nanodiamonds (NDs) have also been investigated for comparison.
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12. |
- Ahmed, Taha, et al.
(författare)
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Optical Quantum Confinement in Ultrasmall ZnO and the Effect of Size on Their Photocatalytic Activity
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:11, s. 6395-6404
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Tidskriftsartikel (refereegranskat)abstract
- Zinc oxide is a well-known metal oxide semiconductor with a wide direct band gap that offers a promising alternative to titanium oxide in photocatalytic applications. ZnO is studied here as quantum dots (QDs) in colloidal suspensions, where ultrasmall nanoparticles of ZnO show optical quantum confinement with a band gap opening for particles below 9 nm in diameter from the shift of the band edge energies. The optical properties of growing ZnO QDs are determined with Tauc analysis, and a system of QDs for the treatment and degradation of distributed threats is analyzed using an organic probe molecule, methylene blue, whose UV/vis spectrum is analyzed in some detail. The effect of optical properties of the QDs and the kinetics of dye degradation are quantified for low-dimensional ZnO materials in the range of 3-8 nm and show a substantial increase in photocatalytic activity compared to larger ZnO particles. This is attributed to a combined effect from the increased surface area as well as a quantum confinement effect that goes beyond the increased surface area. The results show a significantly higher photocatalytic activity for the QDs between 3 and 6 nm with a complete decolorization of the organic probe molecule, while QDs from 6 nm and upward in diameter show signs of competing reduction reactions. Our study shows that ultrasmall ZnO particles have a reactivity beyond that which is expected because of their increased surface area and also demonstrates size-dependent reaction pathways, which introduces the possibility for size-selective catalysis.
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13. |
- Ai, Yuejie, et al.
(författare)
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Hydrophobicity and Hydrophilicity Balance Determines Shape Selectivity of Suzuki Coupling Reactions Inside Pd@meso-SiO2 Nanoreactor
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:19, s. 10244-10251
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Tidskriftsartikel (refereegranskat)abstract
- Molecular sorting and catalysis directed by shape selectivity have been extensively applied in porous extended frameworks for a low-carbon, predictable, renewable component of modern industry. A comprehensive understanding of the underlying recognition mechanism toward different shapes is unfortunately still missing, owing to the lack of structural and dynamic information under operating conditions. We demonstrate here that such difficulties can be overcome by state-of-the-art molecular dynamics simulations which provide atomistic details that are not accessible experimentally, as exemplified by our interpretation for the experimentally observed aggregation induced shape selectivity for Suzuki C-C coupling reaction catalyzed by Pd particles in mesoporous silica. It is found that both aggregation ability and aggregating pattern of the reactants play the decisive role in controlling the shape selectivity, which are in turn determined by the balance between the hydrophobicity and hydrophilicity of the reactants, or in other words, by the balance between the noncovalent hydrogen bonding interaction and van der Waals forces. A general rule that allows prediction of the shape selectivity of a reactant has been proposed and verified against experiments. We show that molecular modeling is a powerful tool for rational design of new mesoporous systems and for the control of catalytic reactions that are important for the petrochemical industry.
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14. |
- Akola, J., et al.
(författare)
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Thiolate-Protected Au-25 Superatoms as Building Blocks: Dimers and Crystals
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:38, s. 15986-15994
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Tidskriftsartikel (refereegranskat)abstract
- A particularly stable thiolate-protected gold nanocluster, Au-25(SR)(18), was structurally characterized from X-ray crystallography in 2008, and concomitantly its electronic and optical properties were analyzed via density functional theory. The robust geometry and a well-understood electronic structure of this cluster motivate explorations of properties of extended systems made out of Au-25(SR)(18) building blocks. As a first step in this direction, we analyze here structural, vibrational, electronic, and optical properties of the Au-25 cluster anion as it was observed in the crystalline environment and predict properties of cluster dimers, where the Au-25 units are linked together. via an aromatic dithiolate linker. We show that properties of each Au-25 unit of the dimer can be quite independently modified from the other by doping with a nonmagnetic (Pd) or magnetic (Mn) metal atom. We anticipate that material systems with interesting properties could be made from these building blocks, provided that a suitable chemistry for their controlled linking can be found.
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15. |
- Aktekin, Burak, et al.
(författare)
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Understanding the Capacity Loss in LiNi0.5Mn1.5O4-Li4Ti5O12 Lithium-Ion Cells at Ambient and Elevated Temperatures
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:21, s. 11234-11248
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Tidskriftsartikel (refereegranskat)abstract
- The high-voltage spinel LiNi0.5Mn1.5O4, (LNMO) is an attractive positive electrode because of its operating voltage around 4.7 V (vs Li/Li+) and high power capability. However, problems including electrolyte decomposition at high voltage and transition metal dissolution, especially at elevated temperatures, have limited its potential use in practical full cells. In this paper, a fundamental study for LNMO parallel to Li4Ti5O12 (LTO) full cells has been performed to understand the effect of different capacity fading mechanisms contributing to overall cell failure. Electrochemical characterization of cells in different configurations (regular full cells, back-to-back pseudo-full cells, and 3-electrode full cells) combined with an intermittent current interruption technique have been performed. Capacity fade in the full cell configuration was mainly due to progressively limited lithiation of electrodes caused by a more severe degree of parasitic reactions at the LTO electrode, while the contributions from active mass loss from LNMO or increases in internal cell resistance were minor. A comparison of cell formats constructed with and without the possibility of cross-talk indicates that the parasitic reactions on LTO occur because of the transfer of reaction products from the LNMO side. The efficiency of LTO is more sensitive to temperature, causing a dramatic increase in the fading rate at 55 degrees C. These observations show how important the electrode interactions (cross-talk) can be for the overall cell behavior. Additionally, internal resistance measurements showed that the positive electrode was mainly responsible for the increase of resistance over cycling, especially at 55 degrees C. Surface characterization showed that LNMO surface layers were relatively thin when compared with the solid electrolyte interphase (SEI) on LTO. The SEI on LTO does not contribute significantly to overall internal resistance even though these films are relatively thick. X-ray absorption near-edge spectroscopy measurements showed that the Mn and Ni observed on the anode were not in the metallic state; the presence of elemental metals in the SEI is therefore not implicated in the observed fading mechanism through a simple reduction process of migrated metal cations.
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16. |
- Al-Shammari, Rusul M., et al.
(författare)
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Tunable Wettability of Ferroelectric Lithium Niobate Surfaces : The Role of Engineered Microstructure and Tailored Metallic Nanostructures
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 121:12, s. 6643-6649
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Tidskriftsartikel (refereegranskat)abstract
- An important aspect of optimizing micro- and optofluidic devices for lab on -a-chip systems is the ability to engineer materials properties including surface structure and charge to control wettability. Biocompatible ferroelectric lithium niobate (LN), which is well-known for acoustic and nonlinear optical applications, has recently found potential micro- and optofluidic applications. However, the tunable wettability of such substrates has yet to be explored in detail. Here, we show that the contact angle of LN substrates can be reproducibly tailored between similar to 7 degrees and similar to 421 degrees by controlling the surface topography and chemistry at the nano- and micrometer scale via ferroelectric domain and polarization engineering and polarization-directed photoassisted deposition of metallic nanostructures.
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17. |
- Alarcon, Hugo, et al.
(författare)
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Modification of nanostructured TiO2 electrodes by electrochemical Al3+ insertion : Effects on dye-sensitized solar cell performance
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:35, s. 13267-13274
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured TiO2 films were modified by insertion with aluminum ions using an electrochemical process. After heat treatment these films were found suitable as electrodes in dye-sensitized solar cells. By means of a catechol adsorption test, as well as photoelectron spectroscopy (PES), it was demonstrated that the density of Ti atoms at the metal oxide/electrolyte interface is reduced after Al modification. There is, however, not a complete coverage of aluminum oxide onto the TiO2, but the results rather suggest either the formation of a mixed Al-Ti oxide surface layer or formation of a partial aluminum oxide coating. No new phase could, however, be detected. In solar cells incorporating Al-modified TiO2 electrodes, both electron lifetimes and electron transport times were increased. At high concentrations of inserted aluminum ions, the quantum efficiency for electron injection was significantly decreased. Results are discussed at the hand of different models: A multiple trapping model, which can explain slower kinetics by the creation of additional traps during Al insertion, and a surface layer model, which can explain the reduced recombination rate, as well as the reduced injection efficiency, by the formation of a blocking layer.
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18. |
- Albertin, Stefano, et al.
(författare)
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Oxidation and Reduction of Ir(100) Studied by High-Energy Surface X-ray Diffraction
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:11, s. 5244-5255
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation and reduction of an Ir(100) surface using 2.5, 5, and 10 mbar O2 partial pressure and a sample temperature of 775 K have been studied by using high-energy surface X-ray diffraction (HESXRD) which allowed to record large volumes of reciprocal space in short time periods. The complex 3D diffraction patterns could be disentangled in a stepwise procedure. For the 2.5mbar experiment the measurements indicate the formation of an Ir(100)-O c(2 × 2) oxygen superstructure along with the onset of epitaxial IrO2(110) bulk oxide formation. For the 5 and 10 mbar O2 partial pressures the formation of additional IrO2 bulk oxide epitaxies with (100) and (101) orientations as well as of polycrystalline IrO2 was observed. Upon CO reduction, we found the IrO2 islands to be reduced into epitaxial and metallic Ir(111) and (221) oriented islands.
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19. |
- Albinsson, David, 1990, et al.
(författare)
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Heterodimers for in Situ Plasmonic Spectroscopy: Cu Nanoparticle Oxidation Kinetics, Kirkendall Effect, and Compensation in the Arrhenius Parameters
- 2019
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:10, s. 6284-6293
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Tidskriftsartikel (refereegranskat)abstract
- The ability to study oxidation, reduction, and other chemical transformations of nanoparticles in real time and under realistic conditions is a nontrivial task due to their small dimensions and the often challenging environment in terms of temperature and pressure. For scrutinizing oxidation of metal nanoparticles, visible light optical spectroscopy based on the plasmonic properties of the metal has been established as a suitable method. However, directly relying on the plasmonic resonance of metal nanoparticles as a built-in probe to track oxidation has a number of drawbacks, including the loss of optical contrast in the late oxidation stages. To address these intrinsic limitations, we present a plasmonic heterodimer-based nanospectroscopy approach, which enables continuous self-referencing by using polarized light to eliminate parasitic signals and provides large optical contrast all the way to complete oxidation. Using Au-Cu heterodimers and combining experiments with finite-difference time-domain simulations, we quantitatively analyze the oxidation kinetics of ca. 30 nm sized Cu nanoparticles up to complete oxidation. Taking the Kirkendall effect into account, we extract the corresponding apparent Arrhenius parameters at various extents of oxidation and find that they exhibit a significant compensation effect, implying that changes in the oxidation mechanism occur as oxidation progresses and the structure of the formed oxide evolves. In a wider perspective, our work promotes the use of model-system-type in situ optical plasmonic spectroscopy experiments in combination with electrodynamics simulations to quantitatively analyze and mechanistically interpret oxidation of metal nanoparticles and the corresponding kinetics in demanding chemical environments, such as in heterogeneous catalysis.
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20. |
- Alcantara, K. Suarez, et al.
(författare)
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3CaH(2)+4MgB(2) + CaF2 Reactive Hydride Composite as a Potential Hydrogen Storage Material: Hydrogenation and Dehydrogenation Pathway
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:12, s. 7207-7212
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Tidskriftsartikel (refereegranskat)abstract
- A reactive hydride composite (RHC) with initial composition 3CaH(2) + 4MgB(2) + CaF2 was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2 and Ca(BH4)(2). The main function of CaF2 in the 3CaH(2) + 4MgB(2) + CaF2 RHC is as a dopant for the hydrogenation and dehydrogenation reactions.
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21. |
- Alegret, Joan, 1977, et al.
(författare)
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Plasmonic properties of silver trimers with trigonal symmetry fabricated by electron-beam lithography
- 2008
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:37, s. 14313-14317
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the dipolar plasmon modes of nanoparticle trimers formed by three equal silver disks of diameter D = 100 nm located on the vertexes of an equilateral triangle. Samples were fabricated by electron-beam lithography and studied experimentally by dark-field spectroscopy. The results are found to be in good agreement with electrodynamical simulations based on the discrete dipole approximation (DDA). Similar to nanoparticle dimers, the trimer system exhibits two hybridized dipole resonances to the red and to the blue of the single particle resonance. However, the far-field spectra are polarization-insensitive for light incident normal to the plane of the trimer, and the peak shifts, which occur as the edge-to-edge distance d between the particles decrease, are smaller than for dimers. Moreover, we find that the dipolar displacement patterns are well described by linear combinations of bonding and antibonding symmetry adapted coordinates obtained through symmetry analysis based on the ideal D-3h point-group.
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22. |
- Ali, Ehesan, et al.
(författare)
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Tuning the Magnetic Interaction between Manganese Porphyrins and Ferromagnetic Co Substrate through Dedicated Control of the Adsorption
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:32, s. 14381-14383
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Tidskriftsartikel (refereegranskat)abstract
- We report, on the basis of density-functional theory+U (DFT+U) calculations that metalloporphyrins can adsorb on ferromagnetic metal surfaces in two distinct configurations. Two separate adsorption minima are obtained for manganese porphyrin (MnP) on Co from our DFT+U total energy calculations, which correspond to strong and weak adsorption strengths, respectively. By steering the nature of adsorption, we find that distinct chemical interactions as well as magnetic exchange interactions between the metalloporphyrin and the metal surface can be realized. We furthermore show that a switching of the MnP molecule's spin state can occur even for the weakly adsorbed case. This new discovery opens up prospects for engineering the chemical and magnetic exchange interaction in new functionalized spintronic materials.
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23. |
- Ali-Löytty, Harri, et al.
(författare)
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Chemical Dissolution of Pt(111) during Potential Cycling under Negative pH Conditions Studied by Operando X-ray Photoelectron Spectroscopy
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:41, s. 25128-25134
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Tidskriftsartikel (refereegranskat)abstract
- Dissolution of a platinum catalyst is a major degradation mechanism of fuel cells, but the exact reaction mechanism has remained unclear. Here, electrochemical ambient pressure X-ray photoelectron spectroscopy (EC-APXPS) was utilized to provide direct information on chemical species on a single-crystal Pt(111) electrode under extremely low pH conditions. Measurements were conducted using a novel condensed electrolyte film electrochemical cell applying work function measurement as a loss-free probe for electrochemical potential. We show that platinum can dissolve chemically as Pt2+ ion during potential cycling and redeposit as Pt2+ at the onset potential for cathodic reactions. The dissolution of Pt does not require electrochemical oxidation via oxide place exchange. In contrast, the adsorption of oxygenated species (OH* or O*) at the onset potential for anodic reactions is a sufficient prerequisite to the dissolution. These results provide new insight into the degradation mechanism of Pt under extremely low pH conditions, predicted by the Pourbaix diagram, having practical applications to the durability of Pt-based catalysts in electrochemical energy conversion devices.
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24. |
- Amft, Martin, et al.
(författare)
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A Molecular Mechanism for the Water-Hydroxyl Balance during Wetting of TiO2
- 2013
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:33, s. 17078-17083
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Tidskriftsartikel (refereegranskat)abstract
- We show that the formation of the wetting layer and the experimentally observed continuous shift of the H2O-OH balance toward molecular water at increasing coverage on a TiO2(110) surface can be rationalized on a molecular level. The mechanism is based on the initial formation of stable hydroxyl pairs, a repulsive interaction between these pairs, and an attractive interaction with respect to water molecules. The experimental data are obtained by synchrotron radiation photoelectron spectroscopy and interpreted with the aid of density functional theory calculations and Monte Carlo simulations.
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25. |
- Amidani, Lucia, et al.
(författare)
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Oxygen K-Edge X-ray Absorption Spectra of ThO2 and CeO2 : Experiment, Interpretation, and Structural Effects
- 2023
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:6, s. 3077-3084
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental oxygen K-edge spectra of ThO2 and CeO2 are presented and interpreted based on density functional theory (DFT). The contribution of d and f orbitals to the O Kedge spectrum is identified as well-distinguished peaks, the presence of which evidences the strong hybridization of Th and Ce metal centers with O orbitals. The sensitivity of the O K-edge to both f- and d-states in the absence of a core-hole on the metal ion results in an insightful overview of the electronic structure involved in the chemical bond. In particular, the large bandwidth of the Th 5f band as compared to the Ce 4f band is observed as a set of wider and more substantial set of peaks in the O K-edge, confirming the stronger hybridization of the former with O orbitals. The peak ascribed to the 5f band of ThO2 is found at higher energy than the 6d band, as predicted from DFT calculations on actinide dioxides. To highlight the sensitivity and the potential use of the O K-edge for the characterization of ThO2-based systems, the sensitivity of the spectrum to structural changes such as lattice expansion and size reduction are calculated and discussed.
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26. |
- Amorim, Rodrigo G., et al.
(författare)
-
Boosting DNA Recognition Sensitivity of Graphene Nanogaps through Nitrogen Edge Functionalization
- 2016
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:34, s. 19384-19388
-
Tidskriftsartikel (refereegranskat)abstract
- One of the challenges for next generation DNA sequencing is to have a robust, stable, and reproducible nanodevice. In this work, we propose how to improve the sensing of DNA nucleobase using functionalized graphene nanogap as a solid state device. Two types of edge functionalization, namely, either hydrogen or nitrogen, were considered. We showed that, independent of species involved in the edge passivation, the highest-to-lowest order of the nucleobase transmissions is not altered, but the intensity is affected by several orders of magnitude. Our results show that nitrogen edge tends to p-dope graphene, and most importantly, it contributes with resonance states close to the Fermi level, which can be associated with the increased conductance. Finally, the translocation process of nucleobases passing through the nanogap was also investigated by varying their position from a certain height (from +3 to -3 angstrom) with respect to the graphene sheet to show that nitrogen-terminated sheets have enhanced sensitivity, as moving the nucleobase by approximately 1 angstrom reduces the conductance by up to 3 orders of magnitude.
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27. |
- Andersson, Klas J., et al.
(författare)
-
Preparation, Structure, and Orientation of Pyrite FeS2{100} Surfaces : Anisotropy, Sulfur Monomers, Dimer Vacancies, and a Possible FeS Surface Phase
- 2014
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:38, s. 21896-21903
-
Tidskriftsartikel (refereegranskat)abstract
- Sulfur dimer (S-2(2-)) terminated pyrite FeS2{100} surfaces with a low energy electron diffraction (LEED) pattern of 2 x 1 symmetry are reported. The 2 X 1 symmetry correlates with the orientation of the anisotropic surface structure and external symmetry of macroscopic striations on the pyrite cube face. The basic condition to form these surfaces is a mild 200 V Ne+ sputter-cleaning procedure followed by a 570 K anneal of the sample in a 10(-7) Ton S-2(g) atmosphere. Controlled amounts of surface sulfur monomers (S2-) can be introduced by mild sputtering of the sulfur dimer terminated surfaces. At low monomer concentrations the surface displays the same characteristic 1 x 1 LEED pattern as that for fracture-generated surfaces. With increasing sulfur depletion, a (1/ root 2 x 1/ root 2)R45 degrees LEED pattern emerges, and soft X-ray photoelectron spectroscopy (XPS) results show a sulfur dinner deficient near-surface region and a new high binding energy sulfur spectral component suggesting the presence of local coordination environments where sulfur monomers are coordinated by four Fe ions compared to three as in the pyrite structure. The plausible formation of a defective FeS-like surface phase where monomeric sulfurs are coordinated by four Fe ions, and bond counting energetics favoring surface sulfur monomer recombination around Fe vacancy sites on pyrite FeS2{100}, both imply surface sulfur dimer vacancy sites with unique adsorption and reactivity properties. Taken together, our results suggest a very rich and dynamic defect structural landscape at pyrite FeS2{100} surfaces with direct implications for its surface chemical activity.
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28. |
- Andersson, Mikael, et al.
(författare)
-
Interplay between the Reorientational Dynamics of the B3H8- Anion and the Structure in KB3H8
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:7, s. 3716-3724
-
Tidskriftsartikel (refereegranskat)abstract
- The structure and reorientational dynamics of KB3H8 were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the alpha'- and beta-polymorphs. Furthermore, it was found that the [B3H8](-) anion undergoes different reorientational motions in the three polymorphs alpha, alpha', and beta. In alpha-KB3H8, the [B3H8](-) anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C-2 symmetry axis of the [B3H8](-) anion upon transitioning to alpha'-KB3H8. After transitioning to beta-KB3H8, the [B3H8](-) anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of beta-KB3H8 deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B3H8](-) anion facilitates the K+ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K+ conductivity.
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29. |
- Andersson, M., et al.
(författare)
-
Microemulsion-mediated room-temperature synthesis of high-surface-area rutile and its photocatalytic performance
- 2007
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:18, s. 6789-6797
-
Tidskriftsartikel (refereegranskat)abstract
- Nanosized titania having the rutile crystalline structure was synthesized at room temperature using a microemulsion-mediated system. The formed rutile particles had a diameter of 3 nm, which corresponds well with the droplet size of the water-in-oil microemulsion used for their preparation. The crystallinity was monitored by both X-ray diffraction (XRD) and electron diffraction, together with dark-field electron microscopy (TEM) and high-resolution TEM. The rutile had a high specific surface area (similar to 300 m(2)/g) according to N-2 adsorption and the BET equation. To our knowledge, this is the highest specific surface area ever reported for rutile. The rutile crystals aligned in a specific crystallographic direction forming elongated aggregates 200-1000 nm in size, as observed by TEM and high-resolution TEM. The titania formation was followed in situ using dynamic light scattering and UV-vis spectroscopy, and together with TEM and XRD performed on samples collected throughout the duration of the titania synthesis, the results gave support for a formation scheme involving the initial formation of amorphous titania followed by crystallization of rutile. The photocatalytic performance of the formed material was evaluated by in situ Fourier transform infrared spectroscopy and compared to that of a rutile sample having a lower specific surface area (similar to 40 m(2)/g). The TEM and formate adsorption experiments revealed that the high-surface-area rutile had a much higher fraction of (101) facets than the low-surface-area sample, which predominantly exposed (110) facets. In particular, a new bidentate formate (mu-formate) species bridge-bonded to the (101) facet could be identified with characteristic bands at 1547 and 1387 cm(-1). The photodegradation rate of this species was found to be similar to the mu-formate species on the (110) facet. However, the overall formate degradation rate was larger on the high-surface-area rutile sample because of a high concentration of the more readily photodegradable monodentate formate (eta(1)-formate) on that sample.
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30. |
- Andersson, Mikael, 1986, et al.
(författare)
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Promoting Persistent Superionic Conductivity in Sodium Monocarba-closo-dodecaborate NaCB11H12 via Confinement within Nanoporous Silica
- 2021
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:30, s. 16689-16699
-
Tidskriftsartikel (refereegranskat)abstract
- Superionic phases of bulk anhydrous salts based on large cluster-like polyhedral (carba)borate anions are generally stable only well above room temperature, rendering them unsuitable as solid-state electrolytes in energy-storage devices that typically operate at close to room temperature. To unlock their technological potential, strategies are needed to stabilize these superionic properties down to subambient temperatures. One such strategy involves altering the bulk properties by confinement within nanoporous insulators. In the current study, the unique structural and ion dynamical properties of an exemplary salt, NaCB11H12, nanodispersed within porous, high-surface-area silica via salt-solution infiltration were studied by differential scanning calorimetry, X-ray powder diffraction, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and impedance spectroscopy. Combined results hint at the formation of a nanoconfined phase that is reminiscent of the high-temperature superionic phase of bulk NaCB11H12, with dynamically disordered CB11H12-anions exhibiting liquid-like reorientational mobilities. However, in contrast to this high-temperature bulk phase, the nanoconfined NaCB11H12 phase with rotationally fluid anions persists down to cryogenic temperatures. Moreover, the high anion mobilities promoted fast-cation diffusion, yielding Na+ superionic conductivities of similar to 0.3 mS/cm at room temperature, with higher values likely attainable via future optimization. It is expected that this successful strategy for conductivity enhancement could be applied as well to other related polyhedral (carba)borate-based salts. Thus, these results present a new route to effectively utilize these types of superionic salts as solid-state electrolytes in future battery applications.
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31. |
- Andersson, Patrik U, 1970, et al.
(författare)
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Water Condensation on Graphite Studied by Elastic Helium Scattering and Molecular Dynamics Simulations
- 2007
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15258-15266
-
Tidskriftsartikel (refereegranskat)abstract
- Formation of water/ice layers on graphite has been studied in the temperature range from 90 to 180 K by elastic helium scattering, light scattering, and molecular dynamics simulations. Combined helium- and light-scattering experiments show that an ice film that wets the graphite surface is formed at surface temperatures of 100-140 K, whereas three-dimensional ice structures are formed at 140-180 K. Desorption of adsorbed water molecules competes with water incorporation into the ice film, and the ice formation rate is strongly temperature dependent. At 150 K, ice-layer formation takes place at the same time scale as layer reconstruction, and its properties are sensitive to the water deposition rate. The experimental results are compared with kinetics models, and the Johnston-Mehl-Avrami-Kolmogorov model is concluded to well describe the ice-layer formation kinetics in the whole temperature range. Molecular dynamics simulations of water-cluster formation on graphite at 90-180 K show that water molecules and small clusters are highly mobile on the surface, which rapidly results in the nucleation of large and less mobile clusters on the surface. Clusters formed at low temperature tend to have the most molecules in direct contact with the uppermost graphite layer, while multilayer cluster structures are preferred at high temperatures. The results are discussed and compared with earlier studies of water ice formation on solid surfaces.
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32. |
- Andreasson, Joakim, 1973, et al.
(författare)
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A molecule-based 1 : 2 digital demultiplexer
- 2007
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:38, s. 14274-14278
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Tidskriftsartikel (refereegranskat)abstract
- A trichromophoric molecule consisting of a porphyrin linked to both a dihydropyrene and a dihydroindolizine-type photochrome, in combination with a third harmonic generating crystal, functions as a 1:2 digital demultiplexer with photonic inputs and outputs. Each of the two photochromes may be cycled independently between two metastable forms, leading to four photoisomers, three of which are used in the demultiplexer. These isomers interact photochemically with the porphyrin in order to yield the demultiplexer function. With the address input (1064-nm light) turned off, one Output of the device (porphyrin fluorescence) tracks the state of the data input (532-nm light). When the address input is turned on, the second output (absorbance at 572 nm) tracks the state of the data input, while the first output remains off. The demultiplexer does not require chemical or electrical inputs, and can cycle through its operational sequences multiple times.
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33. |
- Andrén, Daniel, 1991, et al.
(författare)
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Surface Interactions of Gold Nanoparticles Optically Trapped against an Interface
- 2019
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:26, s. 16406-16414
-
Tidskriftsartikel (refereegranskat)abstract
- Particles that diffuse in close proximity to a surface are expected to behave differently than in free solution because the surface interaction will influence a number of physical properties, including the hydrodynamic, optical, and thermal characteristics of the particle. Understanding the influence of such effects is particularly important in view of the increasing interest in laser tweezing of colloidal resonant nanoparticles for applications such as nanomotors and optical printing and for investigations of unconventional optical forces. Therefore, we used total internal reflection microscopy to probe the interaction between a glass surface and individual ∼100 nm gold nanoparticles trapped by laser tweezers. The results show that particles can be optically confined at controllable distances ranging between ∼30 and ∼90 nm from the surface, depending on the radiation pressure of the trapping laser and the ionic screening of the surrounding liquid. Moreover, the full particle-surface distance probability distribution can be obtained for single nanoparticles by analyzing temporal signal fluctuations. The experimental results are in excellent agreement with Brownian dynamics simulations that take the full force field and photothermal heating into account. At the observed particle-surface distances, translational friction coefficients increase by up to 60% compared to freely diffusing particles, whereas the rotational friction and thermal dissipation are much less affected. The methodology used here is general and can be adapted to a range of single nanoparticle-surface interaction investigations.
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34. |
- Angenendt, Knut, 1982, et al.
(författare)
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Ionic liquid structures from large DFT calculations using mindless configurations
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:48, s. 20577-20582
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Tidskriftsartikel (refereegranskat)abstract
- Three different popular imidazolium based ionic liquids (ILs); EMI-BF4, EMI-PF6, and EMI-TFSI, have been modeled by DFT calculations (B3LYP/6-311+G*) using large, up to 130 atom cluster models, for a better understanding of the structure and ion ion interactions in these ILs and ILs in general. Particular emphasis has been put on the role of appropriate starting structures and how the present large models differ from the ion-pair models of ILs generally used. The system size normalized ion ion interaction energies are shown to converge rapidly, and conformational equilibria and higher order properties like IR spectra are shown to be valuable as quality criteria. The explicit inclusion of an IL environment by the large cluster approach is also compared to using an implicit, continuum, strategy via SCRF C-PCM calculations.
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35. |
- Anikina, Ekaterina, et al.
(författare)
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Tunning Hydrogen Storage Properties of Carbon Ene-Yne Nanosheets through Selected Foreign Metal Functionalization
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:31, s. 16827-16837
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we have employed density functional theory with a range of van der Waals corrections to study geometries, electronic structures, and hydrogen (H-2) storage properties of carbon ene-yne (CEY) decorated with selected alkali (Na, K) and alkaline-earth metals (Mg, Ca). We found that all metals, except Mg, bind strongly by donating a major portion of their valence electrons to the CEY monolayers. Thermal stabilities of representative systems, Ca-decorated CEY monolayers, have been confirmed through ab initio molecular dynamics simulations (AIMD). We showed that each metal cation adsorbs multiple H-2 with binding energies (E-bind) considerably stronger than on pristine CEY. Among various metal dopants, Ca stands out with the adsorption of five H-2 per each Ca having E-bind values within the desirable range for effective adsorption/desorption process. The resulting gravimetric density for CEY@Ca has been found around 6.0 wt % (DFT-D3) and 8.0 wt % (LDA), surpassing the U.S. Department of Energy's 2025 goal of 5.5 wt %. The estimated H-2 desorption temperature in CEY@Ca exceeds substantially the boiling point of liquid nitrogen, which confirms its potential as a practical H-2 storage medium. We have also employed thermodynamic analysis to explore the H-2 adsorption/desorption mechanism at varied conditions of temperature and pressure for real-world applications.
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36. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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A Multiscale Approach to Modeling Plasmonic Nanorod Biosensors
- 2016
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:37, s. 20692-20701
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Tidskriftsartikel (refereegranskat)abstract
- Due to their strongly enhanced optical near fields, plasmonic nanostructures are promising candidates as ultrasensitive label-free sensors of single molecule binding kinetics. However, the interpretation of nanoplasmonic sensing data is complicated by the spatial inhomogeneity of the near-field response and the stochastic nature of molecule-nanoparticle interactions, which makes it difficult to accurately count the number of adsorbed molecules per nanosensor. We combined electromagnetic calculations with stochastic diffusion-reaction simulations in order to investigate how these two sources of noise influence the uncertainty in measured molecular association and dissociation rate constants and concentration for the most common type of plasmonic nanosensor, the nanorod. Using this multiscale in silico tool, we show how to minimize the measurement uncertainty, and we identify the optimum nanorod aspect ratio for quantitative sensing.
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37. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Absorption Enhancement in Lossy Transition Metal Elements of Plasmonic Nanosandwiches
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:38, s. 20522-20529
-
Tidskriftsartikel (refereegranskat)abstract
- Combination of catalytically active transition metals and surface plasmons offers a promising way to drive chemical reactions by converting incident visible light into energetic electron-hole pairs acting as a mediator. In such a reaction enhancement scheme, the conversion efficiency is dependent on light absorption in the metal. Hence, increasing absorption in the plasmonic structure is expected to increase generation of electron-hole pairs and, consequently, the reaction rate. Furthermore, the abundance of energetic electrons might facilitate new reaction pathways. In this work we discuss optical properties of homo- and heterometallic plasmonic nanosandwiches consisting of two parallel disks made of gold and palladium. We show how near-field coupling between the sandwich elements can be used to enhance absorption in one of them. The limits of this enhancement are investigated using finite-difference time-domain simulations. Physical insight is gained through a simple coupled dipole analysis of the nanostructure. For small palladium disks (compared to the gold disk), total absorption enhancement integrated over the near visible solar AM 1.5 spectrum is 8-fold, while for large palladium disks, similar in size to the gold one, it exceeds three.
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38. |
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39. |
- Araujo, Rafael Barros Neves de, et al.
(författare)
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Divulging the Hidden Capacity and Sodiation Kinetics of NaxC6Cl4O2 : A High Voltage Organic Cathode for Sodium Rechargeable Batteries
- 2017
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:26, s. 14027-14036
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Tidskriftsartikel (refereegranskat)abstract
- In the current emerging sustainable organic battery field, quinones are seen as one of the prime candidates for application in rechargeable battery electrodes. Recently, C6Cl4O2, a modified quinone, has been proposed as a high voltage organic cathode. However, the sodium insertion mechanism behind the cell reaction remained unclear due to the nescience of the right crystal structure. Here, the framework of the density functional theory (DFT) together with an evolutionary algorithm was employed to elucidate the crystal structures of the compounds NaxC6Cl4O2 (x = 0.5, 1.0, 1.5 and 2). Along with the usefulness of PBE functional to reflect the experimental potential, also the importance of the hybrid functional to divulge the hidden theoretical capacity is evaluated. We showed that the experimentally observed lower specific capacity is a result of the great stabilization of the intermediate phase Na1.5C6Cl4O2. The calculated activation barriers for the ionic hops are 0.68, 0.40, and 0.31 eV, respectively, for NaC6Cl4O2, Na1.5C6Cl4O2, and Na2C6Cl4O2. These results indicate that the kinetic process must not be a limiting factor upon Na insertion. Finally, the correct prediction of the specific capacity has confirmed that the theoretical strategy used, employing evolutionary simulations together with the hybrid functional framework, can rightly model the thermodynamic process in organic electrode compounds.
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40. |
- Armanious, Antonius, 1981, et al.
(författare)
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Determination of Nanosized Adsorbate Mass in Solution Using Mechanical Resonators: Elimination of the So Far Inseparable Liquid Contribution
- 2021
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:41, s. 22733-22746
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Tidskriftsartikel (refereegranskat)abstract
- Assumption-free mass quantification of nanofilms, nanoparticles, and (supra)molecular adsorbates in a liquid environment remains a key challenge in many branches of science. Mechanical resonators can uniquely determine the mass of essentially any adsorbate; yet, when operating in a liquid environment, the liquid dynamically coupled to the adsorbate contributes significantly to the measured response, which complicates data interpretation and impairs quantitative adsorbate mass determination. Employing the Navier-Stokes equation for liquid velocity in contact with an oscillating surface, we show that the liquid contribution for rigid systems can be eliminated by measuring the response in solutions with identical kinematic viscosity but different densities. Guided by this insight, we used the quartz crystal microbalance (QCM), one of the most widely employed mechanical resonators, to experimentally demonstrate that the kinematic-viscosity matching can be utilized to quantify the dry mass of rigid and in many cases also nonrigid adsorbate systems, including, e.g., rigid nanoparticles, tethered biological nanoparticles (lipid vesicles), as well as highly hydrated polymeric films. For all the adsorbates, the dry mass determined using the kinematic-viscosity matching was within the uncertainty limits of the corresponding mass determined using complementary methods, i.e., QCM in air, scanning electron microscopy, surface plasmon resonance, and theoretical estimations. The same approach applied to the simultaneously measured energy dissipation made it possible to quantify the mechanical properties of the adsorbate and its attachment to the surface, as demonstrated by, for example, probing the hydrodynamic stabilization induced by nanoparticle crowding. In addition to a unique means to quantify the liquid contribution to the measured response of mechanical resonators, we also envision that the kinematic-viscosity-matching approach will open up applications beyond mass determination, including a new means to investigate orientation, spatial distribution, and binding strength of adsorbates without the need for complementary techniques.
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41. |
- Arruda, Lucas M., et al.
(författare)
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Modifying the Magnetic Anisotropy of an Iron Porphyrin Molecule by an on-Surface Ring-Closure Reaction
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 123:23, s. 14547-14555
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of adsorbed metalloporphyrin molecules can be altered or tuned by the substrate, additional axial ligands, or changes to the molecules' macrocycle. These modifications influence the electronic configuration of the fourfold-coordinated central metal ion that is responsible for the metalloporphyrins' magnetic properties. We report a substantial increase in the effective spin moment obtained from sum-rule analysis of X-ray magnetic circular dichroism for an iron metalloporphyrin molecule on Au(111) through its conversion from iron(II)-octaethylporphyrin to iron(II)-tetrabenzoporphyrin in a surface-assisted ring-closure ligand reaction. Density functional theory calculations with additional strong Coulomb correlation (DFT+U) show that the on-surface reaction alters the conformation of the molecule, increasing its planarity and the ion-surface distance. A spin-Hamiltonian fit of the magnetization as a function of field reveals a substantial increase in the intra-atomic magnetic dipole term (T-z) and a decrease in the magnitude of the easy-plane anisotropy upon ring closure. This consequence of the ring closure demonstrates how new magnetic properties can be obtained from on-surface reactions, resulting here in significant modifications to the magnetic anisotropy of the Fe ion, and sheds light onto the molecule-substrate interaction in these systems.
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42. |
- Arvidsson, Adam, 1990, et al.
(författare)
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Influence of Acidity on the Methanol-to-DME Reaction in Zeotypes: A First Principles-Based Microkinetic Study
- 2020
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:27, s. 14658-14663
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Tidskriftsartikel (refereegranskat)abstract
- Acidity is considered a key factor in zeotype-based catalysts. Here, the effect of acidity in the methanol-to-DME reaction is investigated using first-principles calculations and microkinetic modeling, thereby establishing a connection between acididity and kinetics. The CHA, MFI, and BEA frameworks are investigated, and the acidity of the Brønsted hydroxyl group is varied by exchanging a T-site Si with Al, B, Ga, and Fe in the zeolites, along with SAPO-34, Mg-AlPO-34, Zn-AlPO-34, and Ti-AlPO-34 zeotypes with the CHA structure, and as a result, the Brønsted hydroxyl group spans a wide range of acidity. Clear trends in adsorption and transition-state energies are found and by means of linear regression, we obtain scaling relations of relevant energies that are later used as input in a mean-field steady-state microkinetic model. This study confirms that both the shift in frequency of the Brønsted hydroxyl stretch, ΔfOH, caused by adsorption of CO and the ammonia adsorption energy, ΔEammonia, on the Brønsted site are equivalent descriptors for the acidity of the Brønsted acid site and the reactivity of the different zeotypes relevant for the methanol-to-DME reaction. It further shows that a full microkinetic model is needed to accurately describe the reaction over the whole range of temperatures. However, if focusing on low temperatures, where the associative mechanism is dominating the reaction, a simple rate-determining step model is actually able to describe the results with satisfying agreement (deviation of the rate by less than a factor of two).
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43. |
- Asano, Kohta, et al.
(författare)
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Destabilization of Mg Hydride by Self-Organized Nanoclusters in the Immiscible Mg-Ti System
- 2015
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:22, s. 12157-12164
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Tidskriftsartikel (refereegranskat)abstract
- Mg is an attractive hydrogen storage material not only because of its high gravimetric and volumetric hydrogen capacities but also because of it low material costs. However, the hydride of MgH2 is too stable to release hydrogen under moderate conditions. We demonstrate that the formation of nanometer-sized clusters of Mg reduces the stability of MgH2 by the interface energy effect in the immiscible Mg-Ti system. Ti-rich MgxTi1-x (x < 0.5) thin films deposited by magnetron sputtering have a hexagonal close packed (HCP) structure, which forms a face-centered cubic (FCC) hydride phase upon hydrogenation. Positron Doppler broadening depth profiling demonstrates that after hydrogenation, nanometer-sized MgH2 clusters are formed which are coherently embedded in an FCC TiH2 matrix. The P (pressure)-T (optical transmission) isotherms measured by hydrogenography show that these MgH2 clusters are destabilized. This indicates that the formation of nanometer-sized Mg allows for the development of a lightweight and cheap hydrogen storage material with a lower desorption temperature.
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44. |
- Aslandukov, Andrey, et al.
(författare)
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High-Pressure Yttrium Nitride, Y5N14, Featuring Three Distinct Types of Nitrogen Dimers
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 125:32, s. 18077-18084
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Tidskriftsartikel (refereegranskat)abstract
- Yttrium nitride, Y5N14, was synthesized by direct reaction between yttrium and nitrogen at similar to 50 GPa and similar to 2000 K in a laser-heated diamond anvil cell. High-pressure single-crystal X-ray diffraction revealed that the crystal structure of Y5N14 (space group P4/mbm) contains three distinct types of nitrogen dimers. Crystal chemical analysis and ab initio calculations demonstrated that the dimers [N-2](x-) are crystallographically and chemically nonequivalent and possess distinct noninteger formal charges (x) that make Y5N14 unique among known compounds. Theoretical computations showed that Y5N14 has an anion-driven metallicity, with the filled part of its conduction band formed by nitrogen p-states. The compressibility of Y5N14, determined on decompression down to similar to 10 GPa, was found to be uncommonly high for dinitrides containing +3 cations (the bulk modulus K-0 = 137(6) GPa).
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45. |
- Babucci, Melike, et al.
(författare)
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Characterization of a Metal–Organic Framework Zr6O8 Node-Supported Atomically Dispersed Iridium Catalyst for Ethylene Hydrogenation by X-ray Absorption Near-Edge Structure and Infrared Spectroscopies
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:31, s. 16995-17007
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic properties of atomically dispersed supported metals depend on the supports as ligands. We report metal-organic frameworks in the UiO-66 family, synthesized with various ligands that influence the electron-donor properties of the Zr6O8 nodes, including benzene-1,4-dicarboxylate linkers (some with substituents) and formate, acetate, benzoate, and trifluoroacetate. Catalytically active iridium species on the nodes were made by chemisorption of Ir(CO)(2)(acetylacetonato), giving Ir(CO) 2 groups, identified by infrared (IR) and extended X-ray absorption fine structure spectroscopies. The electronic properties of the iridium centers, which are sensitive to the supports as ligands, were characterized with high-energy-resolution fluorescence detection X-ray absorption near-edge spectroscopy (HERFD XANES), distinguishing the supports and giving results correlated with the nu(CO) IR spectra and catalytic activities of partially decarbonylated iridium sites for ethylene hydrogenation at 313 K and atmospheric pressure. The IR spectra of the working catalyst incorporating linkers with NH2 substituents show an initial induction period as reactants changed the iridium ligand environment, after which the catalyst operating in a once-through flow reactor underwent no measurable deactivation for 48 h. Among the results, we emphasize the value of HERFD XANES spectroscopy for the sensitive assessment of the effects of supports as ligands that determine the catalytic properties of atomically dispersed metals.
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46. |
- Babucci, Melike, et al.
(författare)
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Interactions of [BMIM][BF4] with Metal Oxides and Their Consequences on Stability Limits
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:36, s. 20089-20102
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], and high-surface-area metal oxides, SiO2, TiO2, Fe2O3, ZnO, gamma-Al2O3, CeO2, MgO, and La2O3, covering a wide range of point of zero charges (PZC), from pH = 2 to 11, were investigated by combining infrared (IR) spectroscopy with density functional theory (DFT) calculations. The shifts in spectroscopic features of the ionic liquid (IL) upon coating different metal oxides were evaluated to elucidate the interactions between IL and metal oxides as a function of surface acidity. Consequences of these interactions on the short- and long-term thermal stability limits as well as the apparent activation energy (Ea) and rate constant for thermal decomposition of the supported IL were evaluated. Results showed that stability limits and Ea of the IL on each metal oxide significantly decrease with increasing PZC of the metal oxide. Results presented here indicate that the surface acidity strongly controls the IL surface interactions, which determine the material properties, such as thermal stability. Elucidation of these effects offers opportunities for rational design of materials which include direct interactions of ILs with metal oxides, such as solid catalysts with ionic liquid layer (SCILL), and supported ionic liquid phase (SILP) catalysts for catalysis applications or supported ionic liquid membranes (SILM) for separation applications.
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47. |
- Bajaj, Ashima, et al.
(författare)
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Anomalous Effect of Quantum Interference in Organic Spin Filters
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:44, s. 24361-24371
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Tidskriftsartikel (refereegranskat)abstract
- The molecular topology in the single-molecule nanojunctions through which the de Broglie wave propagates plays a crucial role in controlling the molecular conductance. The enhancement and reduction of the conductance in para- and meta-connected molecules due to constructive and destructive quantum interference (QI), respectively, are quite well established. Herein, we investigated the effect of localized spin centers on spin transportation using organic radicals as molecular junctions. The role of the localized spins on the QI as well as on spin filtering capability is investigated employing density functional theory in combination with nonequilibrium Green's function (NEGF-DFT) techniques. Various organic radicals including nitroxy (NO center dot), phenoxy (PO center dot), and methyl (CH2 center dot) attached to the central benzene ring of pentacene with different terminal connections (para and meta) to gold electrodes are examined. Due to more obvious QI effects, para-connected pentacene is found to be more conductive than the meta one. Surprisingly, on incorporating a radical center, along with spin filtering, a significant reversal of QI effects is observed which manifests itself in such a way that the conductance of meta-coupled radicals is found to be more than para-coupled ones by 2 orders of magnitude. The anomaly in QI patterns induced by the radical center is analyzed and discussed in terms of orbital and structural perspectives.
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48. |
- Bakulin, Artem A., et al.
(författare)
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Morphology, Temperature, and Field Dependence Separation in High-Efficiency Solar Cells Based on Polyquinoxaline Copolymer
- 2016
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 120:8, s. 4219-4226
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Tidskriftsartikel (refereegranskat)abstract
- Charge separation and recombination are key processes determining the performance of organic optoelectronic devices. Here we combine photoluminescence and photovoltaic characterization of organic solar cell devices with ultrafast multipulse photocurrent spectroscopy to investigate charge generation mechanisms in the organic photovoltaic devices based on a blend of an alternating polyquinoxaline copolymer with fullerene. The combined use of these techniques enables the determination of the contributions of geminate and bimolecular processes to the solar cell performance. We observe that charge separation is not a temperature-activated process in the studied materials. At the same time, the generation of free charges shows a dear external field and morphology dependence. This indicates that the critical step of charge separation involves the nonequilibrium state that is formed at early times after photoexcitation, when the polaronic localization is not yet complete. This work reveals new aspects of molecular level charge dynamics in the organic light-conversion systems.
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49. |
- Balog, Sandor, et al.
(författare)
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Dynamic Depolarized Light Scattering of Small Round Plasmonic Nanoparticles: When Imperfection is Only Perfect
- 2014
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:31, s. 17968-17974
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Tidskriftsartikel (refereegranskat)abstract
- Although small round gold nanoparticles (Au NPs) possess only a small degree of shape anisotropy, they support localized surface plasmon resonances and exhibit intrinsic optical anisotropy. These inherent features promote depolarized light scattering, whose temporal fluctuations carry information about rotational Brownian dynamics, and thus can be used to describe the size distribution of round Au NPs. We demonstrate that this allows for a much more accurate determination of particle size and polydispersity through depolarized dynamic light scattering when compared to standard particle sizing with light scattering.
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50. |
- Baltrusaitis, J., et al.
(författare)
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Geometry and Electronic Properties of Glycerol Adsorbed on Bare and Transition-Metal Surface-Alloyed Au(111): A Density Functional Theory Study
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:3, s. 1749-1757
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Tidskriftsartikel (refereegranskat)abstract
- Glycerol exists in large amounts owing to its role as a byproduct in biodiesel production, and thanks to its chemical composition, it can be converted into more high-value products, such as mono- and polyethers, esters, diols, acrolein, and others. Hence, predicting glycerol-reactive properties is of utmost importance for designing efficient catalytic processes for its selective (electro)catalytic transformations; however, such an understanding is still far from complete. In this work, we performed quantum chemical calculations to validate a range of dispersion-corrected functionals to accurately predict and interpret structural, electronic, and vibrational properties of glycerol adsorbed on bare and transition-metal surface-alloyed Au(111) surface. optB86b-vdW (van der Waals) was found to have the overall best agreement with experiments concerning lattice constant, bulk stress, surface energy, and methanol adsorption among PBE (Perdew-Burke-Ernzerhof), optB88-vdW, optPBE-vdW, vdW-DF (density functional), vdW-DF2 (density functional 2nd version), and vdW-BEEF (Bayesian error estimation functional). Glycerol adsorption energy is found to correlate well with the calculated d-band center of the transition-metal-containing Au(111) surface layer. OH stretching vibrations are found to be very sensitive of the surface-alloy atom and resulted in large shifts toward lower wavenumbers, when compared to those on bare Au(111). The latter results clearly show that adsorption of glycerol to surface-alloy atoms can be monitored in situ by infrared spectroscopy.
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