High Miller Index Research Articles

Accurate Surface and Finite-Temperature Bulk Properties of Lithium Metal at Large Scales Using Machine Learning Interaction Potentials.

The properties of lithium metal are key parameters in the design of lithium-ion and lithium-metal batteries. They are difficult to probe experimentally due to the high reactivity and low melting point of lithium as well as the microscopic scales at which lithium exists in batteries where it is found to have enhanced strength, with implications for dendrite suppression strategies. Computationally, there is a lack of empirical potentials that are consistently quantitatively accurate across all properties, and ab initio calculations are too costly. In this work, we train a machine learning interaction potential on density functional theory (DFT) data to state-of-the-art accuracy in reproducing experimental and ab initio results across a wide range of simulations at large length and time scales. We accurately predict thermodynamic properties, phonon spectra, temperature dependence of elastic constants, and various surface properties inaccessible using DFT. We establish that there exists a weak Bell-Evans-Polanyi relation correlating the self-adsorption energy and the minimum surface diffusion barrier for high Miller index facets.

Lowering of Schottky Barrier Height in a Vertical Pillar MOSFET by Deuterium Annealing

The Schottky barrier height (Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) is lowered by high-pressure deuterium annealing (HPDA), in a vertical pillar (VP) metal-oxide-semiconductor field effect transistor (MOSFET). Typical device characteristics were comparatively studied before and after HPDA. A change of contact resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> ) at a Schottky junction was also analyzed by using a transmission line method (TLM). Moreover, HPDA effects on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> were characterized on different crystal orientations of silicon, which has a different number of traps. HPDA is more effective to lower the Φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> at (111) orientation than at (100) orientation because a greater number of interface traps can be passivated for an orientation with a high Miller index. Finally, a deuterium peak was physically profiled across the Schottky junction by use of time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Clinical and hemodynamic features of acute pulmonary embolism patients diagnosed in cold weather predicts adverse clinical outcome.

Acute pulmonary embolism (APE) is associated with peak incidence and mortality rate in winter. The present study sought to characterize the clinical and hemodynamic features of cold weather on APE patients. All enrolled 224 APE patients underwent clinical and hemodynamic evaluation and baseline parameters were collected. Recruited patients were grouped by weather pattern on admission into cold and warm weather group. The correlation and prognostic values among cold weather and other variables were analyzed. Compared to warm weather group, patients in cold weather group present with more severe cardiac function, with adverse WHO-functional class (P = 0.032) and higher NT-proBNP concentration [1,853.0 (398.0, 5,237.0) pg/ml vs. 847.5 (56.8, 3,090.5) pg/ml, P = 0.001]. The cold weather group also displayed much critical hemodynamic status and heavier thrombosis load, with higher mPAP (29.1 ± 11.2mmHg vs. 25.6 ± 14.2mmHg, P = 0.045), higher PVR [3.3 (1.7, 6.0) wood units vs. 1.8 (0.9, 3.8) wood units, P < 0.001], higher Miller index (21.4 ± 5.9 vs. 19.1 ± 8.0, P = 0.024), and higher D-dimer levels [2,172.0 (854.5, 3,072.5) mg/L vs. 1,094.5 (210.5, 2,914.5) mg/L, P = 0.008]. Besides, cold weather showed well correlation with the above variables. Survival analysis showed APE patients in cold weather had significantly higher clinical worsening event rate (P = 0.010) and could be an independent predictor of adverse clinical outcome in the multivariate analysis (HR 2.629; 95% CI 1.127, 6.135; P = 0.025). APE patients in cold weather were associated with thrombus overload, cardiac dysfunction, hemodynamic collapse and higher clinical worsening event rate. Cold weather proves to be an independent predictor of adverse clinical outcome.

Smallest Stable Si/SiO_{2} Interface that Suppresses Quantum Tunneling from Machine-Learning-Based Global Search.

While the downscaling of size for field effect transistors is highly desirable for computation efficiency, quantum tunneling at the Si/SiO_{2} interface becomes the leading concern when approaching the nanometer scale. By developing a machine-learning-based global search method, we now reveal all the likely Si/SiO_{2} interface structures from thousands of candidates. Two high Miller index Si(210) and (211) interfaces, being only ∼1 nm in periodicity, are found to possess good carrier mobility, low carrier trapping, and low interfacial energy. The results provide the basis for fabricating stepped Si surfaces for next-generation transistors.

Unusual Lattice Parameters Behavior for La1.9Ca0.1NiO4+δ at the Temperatures below Oxygen Loss

In this work, we studied the structural features of La1.9Ca0.1NiO4.11, which is considered a promising cathode material for intermediate temperature solid-oxide fuel cells (IT-SOFC). The effect of different pretreatments on the structural characteristics of the sample was studied using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) in order to elucidate the origin of a peculiar change of lattice parameters observed earlier during in situ XRD studies. The XRD studies have shown that anisotropic broadening for reflections with a high Miller index l appears after tempering of a quenched (from 1100 °C) sample at 250 °C. This temperature is too low for the release/incorporation of oxygen into the structure but is sufficient for oxygen migration inside the structure. The HRTEM assisted us in revealing differences in the defect structure after different pretreatments. Based on obtained results, the following possible explanation was proposed. Observed additional microstrains and non-oriented planar defects as well as a decrease in the coherent scattering region size in the [00l] direction are caused by the non-homogeneous redistribution of interstitial oxygen in the structure during tempering.

An Account of Chiral Metal Surfaces and Their Enantiospecific Chemistry

ConspectusMolecular chirality has been of scientific interest since 1848 when Pasteur demonstrated its direct connection to the rotation of light by solutions of chiral compounds. In the 1960s the connection was made between the chirality of pharmaceutical compounds and their physiological impact; one enantiomer can be therapeutic while the other is toxic. That realization prompted enormous effort in the synthesis of enantiomerically pure compounds for bioactive use (a $300B/yr market). Until relatively recently, metals were ignored as potential substrates for asymmetric surface chemistry because metals have highly symmetric, achiral bulk structures and the premise was that they could not expose chiral surfaces. In 1996, we demonstrated that the high Miller index surfaces of metals can be chiral, existing in two enantiomeric forms M(hkl)R&S, and we hypothesized that they exhibit enantiospecific interactions with chiral adsorbates. Most such intrinsically chiral metal surfaces have ideal structural motifs based on low Miller index terraces separated by kinked monatomic steps. This Account begins with a short tutorial on the ideal and real structures of chiral metal surfaces to provide a firm basis for understanding the origin of their chirality. It then chronicles the evolution of our understanding of their enantiospecific interactions with chiral adsorbates.Detecting, quantifying, and understanding enantiospecific surface chemistry on intrinsically chiral metal surfaces has been far more challenging than coming to the realization that such surfaces exist. The first successes came from measurements and modeling of the enantiospecific adsorption energetics of small chiral molecules such as propylene oxide and trans-1,2-dimethylcyclopropane. These revealed one of the core challenges to observing enantiospecificity, the fact that the enantiospecificities of reaction energetics and barriers tend to be small, i.e., a few kJ/mol. Measurements of the enantiospecific adsorption energetics of R-3-methylcyclohexanone on seven different Cu(hkl)R&S surfaces demonstrated their sensitivity to surface structure, but again revealed variations of only a few kJ/mol. One of the most important advances in our understanding of chiral surface chemistry is that the limitations imposed by weakly enantiospecific interactions can be circumvented by processes with nonlinear kinetics or equilibria. As an example, the surface explosion mechanism of d- and l-tartaric acid decomposition on Cu(hkl)R&S surfaces leads to enantiospecific rates that differ by almost 2 orders of magnitude, in spite of the fact that the rate constants are only weakly enantiospecific. More surprising is the observation that equilibrium adsorption of nonracemic mixtures of d- and l-aspartic acid can lead to autoamplification of enantiomeric excess, even on achiral Cu(111) surfaces. Again, this arises from a nonlinear adsorption isotherm. Most recently, we have developed a high throughput method for identification of the most enantiospecific surface orientation for a given reaction from the continuum of Cu(hkl)R&S surface orientations. These developments, and others described in this Account, firmly establish some of the basic principles of chiral surface chemistry.

General corner charge formula in two-dimensional Cn -symmetric higher-order topological insulators

In this paper, we derive a general formula for the quantized fractional corner charge in two-dimensional ${C}_{n}$-symmetric higher-order topological insulators. We assume that the electronic states can be described by the Wannier functions and that the edges are charge neutral, but we do not assume vanishing bulk electric polarization. We expand the scope of the corner charge formula obtained in previous works by considering more general surface conditions, such as surfaces with higher Miller index and surfaces with surface reconstruction. Our theory is applicable even when the electronic states are largely modulated near system boundaries. It also applies to insulators with nonvanishing bulk polarization, and we find that in such cases the value of the corner charge depends on the surface termination even for the same bulk crystal with ${C}_{3}$ or ${C}_{4}$ symmetry, via a difference in the Wyckoff position of the center of the ${C}_{n}$-symmetric crystal.

Insight into the surface activity of defect structure in \u03b1-MnO2 nanorod: first-principles research

The contribution of defect structure to the catalytic property of α-MnO2 nanorod still keeps mysterious right now. Using microfacet models representing defect structure and bulk models with high Miller index, several parameters, such as cohesive energy, surface energy, density of state, electrostatic potential, et al., have been used to investigate the internal mechanism of their chemical activities by first-principles calculation. The results show that the trend in surface energies of microfacet models follows as Esurface[(112 × 211)] > Esurface[(110 × 211)] > Esurface[(100 × 211)] > Esurface[(111 × 211)] > Esurface[(112 × 112)] > Esurface[(111 × 112)], wherein all of them are larger than that of bulk models. So the chemical activity of defect structure is much more powerful than that of bulk surface. Deep researches on electronic structure show that the excellent chemical activity of microfacet structure has larger value in dipole moments and electrostatic potential than that of bulk surface layer. And the microfacet models possess much more peaks of valent electrons in deformantion electronic density and molecular orbital. Density of state indicates that the excellent chemical activity of defect structure comes from their proper hybridization in p and d orbitals.

Catalytic Performance for the Conversion of Potent Fluorinated Greenhouse Gases by Aluminium Fluorides with Different Morphology

The AlF3 catalysts with controlled morphology (cubic, hexahedron and octahedron) were synthesized via hydrothermal method using different solvents. The dehydrofluorination of 1,1,1,3,3-pentafluoropropane (HFC-245fa) was used as the model reaction to evaluate the catalytic performance of the AlF3 catalysts with different morphology. Results showed that surface area, crystal structure, surface acidic properties together with the chemical composition of the AlF3 catalyst were substantially influenced by the different morphology. XRD results showed that κ-AlF3 crystalline structure was formed when using ethanol as solvent while β-AlF3 crystalline structure was formed when using water as solvent. Among the three prepared AlF3 samples, the AlF3-C catalyst with cubic shape demonstrated not only largest surface area but also most amount of medium-strength surface acid sites, resulting in enhanced reaction activity towards the dehydrofluorination reaction. The characteristic high Miller index crystal planes of (402) and (321) exposed on the cubic shaped AlF3-C catalyst is believed to be the main reason accounting for the high catalytic performance as there are equal amount of Al and F atoms exposed. Moreover, a reaction mechanism describing dedehydrofluorination of HFC-245fa on AlF3 catalyst with equal amount of Al and F atoms exposed on certain crystal planes was proposed.

Morphology Evolution of Hcp Cobalt Nanoparticles Induced by Ru Promoter

AbstractThe modification of the equilibrium morphology to expose active facets of cobalt nanoparticles is essential for tailoring and controlling its catalytic performance. Periodic density functional theory (DFT) was applied to systematically investigate the structure and stability of exposed facets of hcp Co nanoparticles induced by Ru promoter in order to clarify the facet‐dependent equilibrium morphology of hcp Co nanoparticles stabilized by Ru promoter. The adsorption and migration of Ru atom can give rise to the change of the surface energy of exposed facets, thus affecting the equilibrium morphology of the hcp Co nanoparticles. Selectively exposed the high Miller index facets, such as Co(10‐12), Co(11‐20) and Co(11‐21) surfaces, can be tuned by adding Ru promoter. Our theoretical calculation results show that Co(11‐21) becomes the predominantly exposed facet accompanied with the decrease of exposed Co(10‐10) and Co(10‐11) with the increase of Ru loading. Further experimental studies suggest that the area of selectively exposed the Co(10‐11) surface for uniform Co nanoplates loaded with 3.0 wt % Ru will be reduced, which is in agreement with the theoretical predicted result. This work is helpful to design the desired Co‐based FTS catalysts rationally with well‐controlled surface structure.

Atomic structures of high Miller index surfaces of NiO

The two kinds of high Miller index surfaces of NiO.

Atomic structure of high Miller index Si(47 35 7) surface

The structure of high Miller index Si(47 35 7) surface, inclined at 10.7° to the (1 1 0) plane is investigated using low energy electron diffraction, scanning tunneling microscopy (STM) and first principles calculations based on the density functional theory. It was shown that the surface has the 1 × 1 periodicity and is significantly reconstructed, exhibiting the pentameric structures similar to that found on Si(1 1 0) and Ge(1 1 0) surfaces. The tentative surface model is developed on the basis of high-resolution STM images and the universal building block structure recently proposed for Si(1 1 0) and Ge(1 1 0) reconstructed surfaces [Appl. Surf. Sci. 494 (2019) 46].

Quantitative Multilayer Cu(410) Structure and Relaxation Determined by QLEED

Industrially relevant catalytically active surfaces exhibit defects. These defects serve as active sites; expose incoming adsorbates to both high and low coordinated surface atoms; determine morphology, reactivity, energetics, and surface relaxation. These, in turn, affect crystal growth, oxidation, catalysis, and corrosion. Systematic experimental analyses of such surface defects pose challenges, esp., when they do not exhibit order. High Miller index surfaces can provide access to these features and information, albeit indirectly. Here, we show that with quantitative low-energy electron diffraction (QLEED) intensity analyses and density functional theory (DFT) calculations, we can visualize the local atomic configuration, the corresponding electron distribution, and local reactivity. The QLEED-determined Cu(410) structure (Pendry reliability factor RP ≃ 0.0797) exhibits alternating sequences of expansion (+) and contraction (−) (of the first 16 atomic interlayers) relative to the bulk-truncated interlayer spacing of ca. 0.437 Å. The corresponding electron distribution shows smoothening relative to the bulk-determined structure. These results should aid us to further gain an atomic-scale understanding of the nature of defects in materials.

Semiconductor behavior of pentagonal silver nanowires measured under mechanical deformation

In the present work, electrical measurements using in situ transmission electron microscopy (TEM) on pentagonal silver nanowires were performed. Electrical biasing was applied to individual nanowires with and without simultaneous in situ TEM mechanical deformation. The response of the ohmic resistance was measured in the I-V curves. A reduction in the break voltage and the resistance was measured, when the nanowires were subjected to a bending deformation. In situ electric measurements on both, with and without deformation, show a typical semiconductor behavior. Surface scattering of electrons in the nanowires and movement of dislocations act as the main causes of the electrical properties reported herein. In this way, the determination of the surface morphology was carried out by using off-axis electron holography followed by a phase reconstruction and structural modeling. The high Miller-index facets were determined to be the (533) stepped surface plane on all five longitudinal sides of the nanowires. Additionally, due to electrical saturation, a breakdown of the nanowires was observed during the in situ electrical measurements without mechanical deformation.

γ-Fe2O3 as the precursor of iron based catalyst prepared by solid-state reaction at room temperature for Fischer-Tropsch to olefins

Iron catalyst was fabricated via simple solid-state reaction of metal nitrates mixture (Fe, K, Al, Ca, Mg, Sm) with oxalic acid dihydrate at room temperature. Iron catalysts prepared by conventional methods, such as co-precipitation and fusing, are also included as comparison. The performances of catalysts were evaluated by the Fischer-Tropsch Synthesis (FTS) in a fixed bed reactor. The results indicate that uniform nanoparticles were obtained with surface area as high as 38.7 m2/g prepared by solid-state reaction. Following calcination at 500 °C, γ-Fe2O3 were obtained as the catalyst precursor. By contrast, α-Fe2O3 was the main precursor derived from co-precipitation. In addition, γ-Fe2O3 prepared by solid-state reaction facilitates the formation of active phase, Fe5C2 with the exposure of (021) facet. High Miller index surface (021) facilitates the adsorption and the dissociation of CO, which contributes the high activity and high selectivity to light olefins. Consequently, compared with conventional catalysts, solid-state reaction derived catalysts exhibit much higher FTO reaction activity and selectivity to lower olefins. The FTY value of 5.62 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1 was obtained which is almost two times higher than that of catalyst prepared by co-precipitation (3.19 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1) or 3 times higher than that of catalyst prepared by fusing method (1.98 × 10 ̶ 3 molCO gFe̶ 1 s ̶ 1). The selectivity to light olefins of around 40% is obtained which is significantly higher than that of the reference catalysts (25% and 33% respectively). The present study provides a promising pathway to prepare iron based catalysts at room temperature.

Highly Oriented Thin Membrane Fabrication with Hierarchically Porous Zeolite Seed

Nanosized zeolite is widely used as seed for high quality zeolite membranes fabrication, while its complicated synthesis routine limits large-scale productions. In this work, a non-nanosized cubic hierarchically porous TS-1 zeolite (HTS-1), obtained by basic hydrothermal treatment of conventional ellipsoid solid TS-1, is used as seed to prepare highly oriented thin membranes. A capillary condensation phenomenon resulting from the unique hierarchically porous structure benefits gel attachment. Moreover, abundant ledges, kinks, and terraces on the HTS-1 surface promote epitaxial growth of the membrane. In contrast, the solid TS-1 seed induces intergrowth dominantly, which results in a thick TS-1 membrane. The HTS-1 membrane demonstrates superior CO2/N2 separation properties compared to the TS-1 one. It associates with thin oriented membrane morphology, leading to exposure of a high Miller index surface and less diffuse distance and tortuosity. The results suggest beneficial effects of a hierarchically porou...

Promotion of catalytic selectivity on transition metal oxide through restructuring surface lattice

Pursuit of high catalytic selectivity is paramount in the design of catalysts for green chemical processes towards minimizing the production of undesired products. We demonstrated that catalytic selectivity for production of alkene through oxidative dehydrogenation of alkane on transition metal oxides can be promoted through tailoring the surface lattice of the oxide catalyst. Selectivity for production of ethylene through oxidative dehydrogenation (ODH) of ethane on Co3O4 nanocrystals can be substantially increased by 30%–35% via temperature-mediated reconstruction of surface lattice of Co3O4. Co3O4 nanocrystals formed at 800 °C leads to smooth, flat crystal plane with predominantly exposed (111) facet in contrast to high Miller index (311) facet of Co3O4 formed at ≤700 °C, revealed by environmental transmission electron microscopy. Isotope-labelled experiments suggest that the higher catalytic selectivity on the (111) facet results from the lower activity of its surface lattice oxygen atoms. Consistent with these experimental results, DFT calculations suggest low activity of surface lattice oxygen atoms and high activation barriers for adsorption and dissociation of CH bond on the (111) surface in contrast to (311). Upon the activation of CH on (311), the stronger binding of ethylene on more active, under-coordinated surface lattice oxygen atoms of (311) forms a robust “deprotonated ethylene glycol”-like intermediate on (311) with a rate-limiting desorption barrier to the formation of ethylene. Compared to (311), the kinetically favorable desorption of bound ethylene species from (111) surface well rationalized the higher selectivity for production of ethylene on (111) than (311). These findings demonstrate that temperature-mediated tailoring of the surface lattice for a transition metal oxide nanocatalyst is a promising approach in pursuing high selectivity in oxidative dehydrogenation of hydrocarbons.

Hunting the Correlation between Fe5C2 Surfaces and Their Activities on CO: The Descriptor of Bond Valence

To hunt the correlation between the surfaces of Fe5C2 and their corresponding activities, the CO adsorption and dissociation on a series of both low ((010), (001), (110), (111), (111)) and high Miller index surfaces of Fe5C2((221), (411), and (510)) surfaces are systemically investigated. For the CO adsorption, configurations with bonding to surface Fe sites are much stronger than that on C sites. For the CO dissociation, direct C–O cleavage can take place on the (221), (510), (010), and (111) surfaces due to the low activation energy. More importantly, to correlate the surface character and the activity of CO dissociation we proposed a concept of sum bond valence. It is found that the adsorbed CO with more bond valence can dissociate easier, and a linear relationship between the activation energies and the CO bond valence can be established. It can be inferred that the activity of Fe5C2 surfaces for CO dissociation strongly relies on the binding characteristics. The relatively stable (100) and (111) s...

Crystallographic plane and topography-dependent growth of semipolar InGaN nanorods on patterned sapphire substrates by molecular beam epitaxy.

A low-cost, high-efficiency, and catalyst-free method for fabricating well-aligned and uniform semipolar InGaN nanorods (NRs) by molecular beam epitaxy (MBE) is proposed using an optimized patterned sapphire substrate (PSS) with high Miller index crystallographic planes. The dense, obliquely aligned, and high-quality semipolar (11[combining macron]02) InGaN NRs are fabricated on hexagonal pyramid arrays of the PSS for the first time in this work. A unique semipolar (11[combining macron]02) and polar (0001) InGaN NR array composite structure is thus achieved on a hexagonal pyramid PSS. The connected, uniform, and obliquely aligned NRs are formed on the PSS with cylindrical arrays. The cylindrical and hexagonal pyramid arrays of PSSs are structured by the standard photolithography process and etching techniques. Both pattern topography and crystallographic plane of the PSS significantly affect the morphology, dimension, and crystallographic orientation of InGaN NRs. It is clearly demonstrated that the PSS with exposed high Miller index crystallographic planes, with well-organized step-terrace structures, facilitates the growth of ordered and dense semipolar InGaN NRs. This work contributes to the thorough understanding of the nucleation and growth mechanisms of InGaN NRs on a high Miller index plane of the PSS with different topographies, as well as of those of controllably fabricating dense and uniform semipolar NRs, thus facilitating the fabrication of NR-based optoelectronic devices with enhanced performance.

A topological screening heuristic for low-energy, high-index surfaces

Robust ab initio investigations of nanoparticle surface properties require a method to identify candidate low-energy surface facets a priori. By assuming that low-energy surfaces are planes with high atomic density, we devise an efficient algorithm to screen for low-energy surface orientations, even if they have high (hkl) miller indices. We successfully predict the observed low-energy, high-index {1012¯} and {101¯4} surfaces of hematite α-Fe2O3, the {311} surfaces of cuprite Cu2O, and the {112} surfaces of anatase TiO2. We further tabulate candidate low-energy surface orientations for nine of the most common binary oxide structures. Screened surfaces are found to be generally applicable across isostructural compounds with varying chemistries, although relative surface energies between facets may vary based on the preferred coordination of the surface atoms.