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See detailSubtle Fluorination of Conjugated Molecules Enables Stable Nanoscale Assemblies on Metal Surfaces
Niederhausen, Jens; Zhang, Yuan; Kabeer, Fairoja et al

in Journal of Physical Chemistry C (2018), 122(33), 10

In molecular self-assembly on surfaces, the structure is governed by the intricate balance of attractive and repulsive forces between molecules as well as between molecules and the substrate. Frequently ... [more ▼]

In molecular self-assembly on surfaces, the structure is governed by the intricate balance of attractive and repulsive forces between molecules as well as between molecules and the substrate. Frequently, repulsive interactions between molecules adsorbed on a metal surface dominate in the low-coverage regime, and dense self-assembled structures can only be observed close to full monolayer coverage. Here, we demonstrate that fluorination at selected positions of conjugated molecules provides for sufficiently strong, yet nonrigid, H···F bonding capability that (i) enables the formation of stable nanoscale molecular assemblies on a metal surface and (ii) steers the assemblies’ structure. This approach should be generally applicable and will facilitate the construction and study of individual nanoscale molecular assemblies with structures that are not attainable in the high-coverage regime. [less ▲]

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See detailFirst-Principles Study of Alkoxides Adsorbed on Au(111) and Au(110) Surfaces: Assessing the Roles of Noncovalent Interactions and Molecular Structures in Catalysis
Cheenicode Kabeer, Fairoja; Chen, Wei; Madix, Robert J. et al

in Journal of Physical Chemistry C (2017), 121

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption ... [more ▼]

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption process is very systemspecific and there is a clear need to elaborate systematic understanding of important factors that determine catalytic functionality. Here, we investigate the binding of eight molecules, including seven alkoxides and one carboxylate, on the Au(111) and Au(110) surfaces. Our density-functional theory calculations including long-range van der Waals interactions demonstrate the significant role of these “weak” noncovalent forces on the adsorption structures, energetics, and relative adsorbate stabilities. Interestingly, the binding energy trends are insensitive to the surface structure. Instead, the adsorption stability depends strongly on the structural and chemical characteristics of the molecules: linear vs branching configurations, number of unsaturated C−C bonds, bidentate adsorption, and the presence of electronegative atoms. Our calculations help establish the influence of individual and collective chemical factors that determine the catalytic selectivity of alkoxides. [less ▲]

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See detailPhotoelectrochemical Screening of Solar Cell Absorber Layers: Electron Transfer Kinetics and Surface Stabilization
Colombara, Diego UL; Dale, Phillip UL; Kissling, Gabriela P. et al

in Journal of Physical Chemistry C (2016)

edox electrolyte contacts offer a simple way of testing the photocurrent generation/collection efficiency in partially completed thin-film solar cells without the need to complete the entire fabrication ... [more ▼]

edox electrolyte contacts offer a simple way of testing the photocurrent generation/collection efficiency in partially completed thin-film solar cells without the need to complete the entire fabrication process. However, the development of a reliable quantitative method can be complicated by the instability of the semiconductor/electrolyte interface. In the case of Cu(In,Ga)Se2 (CIGSe) solar cells, these problems can be overcome by using samples that have undergone the next processing step in solar cell fabrication, which involves chemical bath deposition of a thin (ca. 50 nm) CdS buffer layer. The choice of redox system is also critical. The frequently used Eu3+/2+ redox couple is not suitable for reliable performance predictions since it suffers from very slow electron transfer kinetics. This leads to the buildup of photogenerated electrons near the interface, resulting in electron–hole recombination. This effect, which can be seen in the transient photocurrent response, has been quantified using intensity-modulated photocurrent spectroscopy (IMPS). The study has demonstrated that the more oxidizing Fe(CN)63–/4– redox system can be used when a CdS buffer layer is deposited on the CIGSe absorber. The wide bandgap CdS acts as a barrier to hole injection, preventing decomposition of the CIGSe and formation of surface recombination centers. The IMPS response of this system shows that there is no recombination; i.e., electron scavenging is very rapid. It is shown that measurements of the external quantum efficiency made using the Fe(CN)63–/4– redox couple with CdS-coated CIGSe layers can provide reliable predictions of the short-circuit currents of the complete solar cells. Similar results have been obtained using CdS-coated GaAs layers, suggesting that the new approach may be widely applicable. [less ▲]

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See detailInteraction of Isophorone with Pd(111): A Combination of Infrared Reflection-Absorption Spectroscopy, Near-Edge X-ray Absorption Fine Structure, and Density Functional Theory Studies
Dostert, Karl-Heinz; O'Brien, Casey P.; Riedel, Wiebke et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2014), 118(48), 27833-27842

Atomistic level understanding of interaction of alpha,beta-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired ... [more ▼]

Atomistic level understanding of interaction of alpha,beta-unsaturated carbonyls with late transition metals is a key prerequisite for rational design of new catalytic materials with the desired selectivity toward C-C or C-O bond hydrogenation. The interaction of this class of compounds with transition metals was investigated on alpha,beta-unsaturated ketone isophorone on Pd(111) as a prototypical system. In this study, infrared reflectionabsorption spectroscopy (IRAS), near-edge X-ray absorption fine structure (NEXAFS) experiments and density functional theory calculations including van der Waals interactions (DFT+vdW) were combined to obtain detailed information on the binding of isophorone to palladium at different coverages and on the effect of preadsorbed hydrogen on the binding and adsorption geometry. According to these experimental observations and the results of theoretical calculations, isophorone adsorbs on Pd(111) in a flat-lying geometry at low coverages. With increasing coverage, both C-C and C-O bonds of isophorone tilt with respect to the surface plane. The tilting is considerably more pronounced for the C-C bond on the pristine Pd(111) surface, indicating a prominent perturbation and structural distortion of the conjugated p system upon interaction with Pd. Preadsorbed hydrogen leads to higher tilting angles of both p bonds, which points to much weaker interaction of isophorone with hydrogen-precovered Pd and suggests the conservation of the in-plane geometry of the conjugated pi system. The results of the DFT+vdW calculations provide further insights into the perturbation of the molecular structure of isophorone on Pd(111). [less ▲]

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See detailHigh-Throughput Investigation of the Geometry and Electronic Structures of Gas-Phase and Crystalline Polycyclic Aromatic Hydrocarbons
Schatschneider, Bohdan; Monaco, Stephen; Liang, Jian-Jie et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2014), 118(34), 19964-19974

The quest for cheap, light, flexible materials for use in electronics applications has resulted in the exploration of soft organic materials as possible candidates, and several polycyclic aromatic ... [more ▼]

The quest for cheap, light, flexible materials for use in electronics applications has resulted in the exploration of soft organic materials as possible candidates, and several polycyclic aromatic hydrocarbons (PAHs) have been shown to be versatile (semi)conductors. In this investigation, dispersion inclusive density functional theory is used to explore all of the current crystalline PAHs within the Cambridge Structure Database (CSD) from both structural and electronic standpoints. Agreement is achieved between the experimental and calculated crystalline structures, as well as the electronic properties. Specifically, variation between the mass densities, unit cell parameters, and intermolecular close contact fractions were within +5\% +/-2\%, and +/-1 of experiment, respectively. It is found that a simple addition of a similar to 1 eV constant to the DFT-PBE gaps provides good agreement with the experimental optical gaps of both gas phase (within +/-2.6\%) and crystalline (within +/-3.5\%) PAHs. Structural and electronic analysis revealed several correlations/trends where ultimately limits in the band gaps as a function of structure are established. Finally, analysis of the difference between band gaps of the isolated molecules and crystals (Delta E-g(Xtal-Mols)) demonstrates that Delta E-g(Xtal-Mols) can be captured qualitatively by PBE and PBE0 functionals, yet significant quantitative deviations remain between these functionals and experiment. [less ▲]

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See detailSingle Second Laser Annealed CuInSe2 Semiconductors from Electrodeposited Precursors as Absorber Layers for Solar Cells
Meadows, Helen UL; Bathia, Ashish; Depredurand, Valérie UL et al

in Journal of Physical Chemistry C (2014), 118 (3)

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See detailUnderstanding Structure and Bonding of Multilayered Metal-Organic Nanostructures
Egger, David A.; Ruiz, Victor G.; Said, Wissam A. et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2013), 117(6), 3055-3061

For organic and hybrid electronic devices, the physicochemical properties of the contained interfaces play a dominant role. To disentangle the various interactions occurring at such heterointerfaces we ... [more ▼]

For organic and hybrid electronic devices, the physicochemical properties of the contained interfaces play a dominant role. To disentangle the various interactions occurring at such heterointerfaces we here model a complex, yet prototypical, three-component system consisting of a Cu-phthalocyanine (CuPc) film on a 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) monolayer adsorbed on Ag(111). The two encountered interfaces are similar, as in both cases there would be no bonding without van der Waals interactions. Still they are also distinctly different, as only at the Ag-(111) PTCDA interface do massive charge-rearrangements occur. Using recently developed theoretical tools, we show that it has become possible to provide atomistic insight into the physical and chemical processes in this comparatively complex nanostructure distinguishing between interactions involving local rearrangements of the charge density and long-range van der Waals attraction. [less ▲]

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See detailCarbon Nanotube Wins the Competitive Binding over Proline-Rich Motif Ligand on SH3 Domain
Zuo, Guanghong; Gu, Wei UL; Fang, Haiping et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2011), 115(25), 12322-12328

The binding competition between a proline-rich motif (PRM) ligand and a hydrophobic nanoparticle, the single-wall carbon nanotube (SWCNT), at the binding pocket of SH3 domain, has been investigated by ... [more ▼]

The binding competition between a proline-rich motif (PRM) ligand and a hydrophobic nanoparticle, the single-wall carbon nanotube (SWCNT), at the binding pocket of SH3 domain, has been investigated by molecular dynamics simulations. It is found that the SWCNT has a very high probability of occupying the binding pocket of the SH3 domain, which prevents the PRM ligand from binding to the pocket. The binding free energy landscapes show that the SWCNT has similar to 0.6 kcal/mol stronger binding affinity than the ligand in the three-way binding competition (SWCNT + ligand + protein). The potent binding affinity between the SWCNT and the SH3 domain is shown to be mainly from the pi-pi stacking interactions between the CNT and aromatic residues in the binding pocket. Our findings show that the existence of hydrophobic particles can greatly reduce the possibility of the regular binding of the ligand with the target protein, suggesting potential toxicity to proteins by hydrophobic nanoscale particles. [less ▲]

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See detailSelf-Consistent Quantum Master Equation Approach to Molecular Transport
Esposito, Massimiliano UL; Galperin, Michael

in Journal of Physical Chemistry C (2010), 114(48),

We propose a self-consistent generalized quantum master equation (GQME) to describe electron transport through molecular junctions. In a previous study [Esposito, M.; Galperin, M. Phys. ReV. B 2009, 79 ... [more ▼]

We propose a self-consistent generalized quantum master equation (GQME) to describe electron transport through molecular junctions. In a previous study [Esposito, M.; Galperin, M. Phys. ReV. B 2009, 79, 205303], we derived a time-nonlocal GQME to cure the lack of broadening effects in Redfield theory. To do so, the free evolution used in the Born-Markov approximation to close the Redfield equation was replaced by a standard Redfield evolution. In the present paper, we propose a backward Redfield evolution leading to a time-local GQME which allows for a self-consistent procedure of the GQME generator. This approach is approximate but properly reproduces the nonequilibrium steady-state density matrix and the currents of an exactly solvable model. The approach is less accurate for higher moments such as the noise. [less ▲]

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See detailDesorption of H2O from Flat and Stepped Pt(111)
Picolin, Alexander; Busse, Carsten; Redinger, Alex UL et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2009), 113(2), 691-697

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface ... [more ▼]

To investigate the effect of steps on H2O binding on a nominal Pt(111) surface, we used thermal desorption spectroscopy of water adsorbed on purposefully nanostructured surfaces: a rippled surface containing densely packed (100)-microfaceted and (111)-microfaceted steps was created using grazing incidence ion bombardment, and a surface with triangular mounds mainly consisting of (111)-microfaceted steps was fabricated through hornoepitaxial growth. These morphologies are determined by scanning tunneling microscopy. We find two additional high -temperature H2O desorption peaks using the rippled surface, whereas only the peak with the highest desorption temperature is present on the (111)-microfaceted mound. Thus, water preferentially binds to steps and especially favors (111)-microfaceted ones. Furthermore, the large step concentration on our nanostructured surfaces precludes the coexistence of a condensed and a diluted phase in a monolayer of water and suppresses the formation of crystalline ice multilayers during heating. [less ▲]

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