Surface Decomposition Research Articles

Low-rank canonical-tensor decomposition of potential energy surfaces: application to grid-based diagrammatic vibrational Green's function theory

ABSTRACTA new method is proposed for a fast evaluation of high-dimensional integrals of potential energy surfaces (PES) that arise in many areas of quantum dynamics. It decomposes a PES into a canonical low-rank tensor format, reducing its integral into a relatively short sum of products of low-dimensional integrals. The decomposition is achieved by the alternating least squares (ALS) algorithm, requiring only a small number of single-point energy evaluations. Therefore, it eradicates a force-constant evaluation as the hotspot of many quantum dynamics simulations and also possibly lifts the curse of dimensionality. This general method is applied to the anharmonic vibrational zero-point and transition energy calculations of molecules using the second-order diagrammatic vibrational many-body Green's function (XVH2) theory with a harmonic-approximation reference. In this application, high dimensional PES and Green's functions are both subjected to a low-rank decomposition. Evaluating the molecular integrals over a low-rank PES and Green's functions as sums of low-dimensional integrals using the Gauss–Hermite quadrature, this canonical-tensor-decomposition-based XVH2 (CT-XVH2) achieves an accuracy of 0.1 cm−1 or higher and nearly an order of magnitude speedup as compared with the original algorithm using force constants for water and formaldehyde.

Morphology Evolution and Degradation of CsPbBr3 Nanocrystals under Blue Light-Emitting Diode Illumination.

Under illumination of light-emitting diode (LED) or sunlight, the green color of all-inorganic CsPbBr3 perovskite nanocrystals (CPB-NCs) often quickly changes to yellow, followed by large photoluminescence (PL) loss. To figure out what is happening on CPB-NCs during the color change process, the morphology, structure, and PL evolutions are systematically investigated by varying the influence factors of illumination, moisture, oxygen, and temperature. We find that the yellow color is mainly originated from the large CPB crystals formed in the illumination process. With maximized isolation of oxygen for the sandwiched film or the uncovered film stored in nitrogen, the color change can be dramatically slowed down whether there is water vapor or not. Under dark condition, the PL emissions are not significantly influenced by the varied relative humidity (RH) levels and temperatures up to 60 °C. Under the precondition of oxygen or air, color change and PL loss become more obvious when increasing the illumination power or RH level, and the large-sized cubic CPB crystals are further evolved into the oval-shaped crystals. We confirm that oxygen is the crucial factor to drive the color change, which has the strong synergistic effect with the illumination and moisture for the degradation of the CPB film. Meanwhile, the surface decomposition and the increased charge trap states occurred in the formed large CPB crystals play important roles for the PL loss.

Intrinsic electronic properties of high-quality wurtzite InN

Recent reports suggested that InN is a highly unusual III-V semiconductor, whose behavior fundamentally differs from that of others. We therefore analyzed its intrinsic electronic properties on the highest available quality InN layers, demonstrating the absence of electron accumulation at the $\left(10\overline{1}0\right)$ cleavage surface and in the bulk. The bulk electron density is governed solely by dopants. Hence, we conclude that InN acts similarly to the other III-V semiconductors and previously reported intriguing effects are related to low crystallinity, surface decomposition, nonstoichiometry, and/or In adlayers.

In Situ AFM Observation of Surface Morphology of Highly Oriented Pyrolytic Graphite in Propylene Carbonate-Based Electrolyte Solutions Containing Lithium and Bivalent Cations

Propylene carbonate (PC) is one of the promising solvents of lithium-ion batteries for use in cold area. Lithium salt concentrated PC and both lithium salt and bivalent salt dissolved PC enabled lithium ion to intercalate at graphite negative electrodes. The key to use PC is a solid electrolyte interphase (SEI). In this study, the SEI formation process on a highly oriented pyrolytic graphite was investigated by in-situ atomic force microscopy (AFM) in 4 mol dm−3 lithium bis(trifluoromethanesulfonyl)amide (LiTFSA)/PC and 1 mol dm−3 LiTFSA + 1.2 mol dm−3 M(TFSA)2 (M = Ca or Mg)/PC. Based on the in-situ AFM observation, the SEI formation processes in 4 mol dm−3 LiTFSA/PC and 1 mol dm−3 LiTFSA + 1.2 mol dm−3 Ca(TFSA)2/PC were the co-intercalation type and that in 1 mol dm−3 LiTFSA + 1.2 mol dm−3 Mg(TFSA)2/PC was the surface decomposition type. Relation between the SEI formation process and the charge–discharge properties was also discussed.

Clay bricks modified by implementing of N‐ and/or C‐TiO 2 : insight into self‐cleaning properties toward fatty contaminant

Clay bricks containing different kinds of titanium dioxide (TiO2) photocatalysts were obtained. The samples have shown high photocatalytic activity during thin layers of oleic acid deposited on their surface decomposition. The self-cleaning effectiveness of the bricks was evaluated on the basis of the water contact angle measurements, or more precisely, wettability rate (WR) changes on the greasy surface layers. It appeared that despite the high-temperature clay firing process (950°C), the presence of quartz and aluminosilicates in clay have caused the inhibition of anatase–rutile transformation. The highest photocatalytic efficiency, determined on the basis of the WR measurements, was observed for TiO2/nitrogen (N) and TiO2/N, carbon (C)-loaded bricks. It should be noted that in the case of the bricks loaded with the TiO2/N,C photocatalyst, the carbon dopant present in the material was burnt out during the high-temperature kiln firing. The N content in latter samples show closely the same results (∼0.03 and ∼0.04 wt% of N for brick loaded with TiO2/N and TiO2/N,C, respectively). In the context of the photocatalytic activity of studied materials, the N presence was found to be one of the most important feature.

The Vertical Mode Decomposition of Surface and Internal Tides in the Presence of a Free Surface and Arbitrary Topography

AbstractThe method of decomposing surface and internal tides determines the expression for internal tide energy, energy flux, and energy conversion. The de facto standard is to define surface tides as depth-averaged pressure and horizontal velocity and internal tides as the residuals. This decomposition, which is equivalent to projecting motion onto vertical modes that obey a rigid lid, is known to produce spurious energy conversion CS through movement of the free surface. Here, motion is instead projected onto modes that obey a linear, free-surface boundary condition. The free-surface modes are shown to obey a more complicated orthogonality condition than rigid-lid modes but are still straightforward to calculate numerically. The resulting decomposition (i) completely eliminates spurious energy conversion CS and (ii) leads to a more precise expression for topographic internal tide generation C, which now depends on horizontal gradients in the vertical structure of the surface tide. Numerical simulations and rough global estimates indicate that corrections to C are a maximum of a few percent. However, CS produces spurious energy flux divergences/convergences in the open ocean, which are the same order of magnitude [O(1–10) mW m−2] as open-ocean internal tide energy dissipation.

Increasing the Capabilities of Computer Process Modeling with Applied Programming Interface

Computer-based process modeling has long been used for simulating the casting of metals. The information from these simulations has allowed metalcasters to reduce the occurrence of some defects that result from the metal’s volumetric contraction or entrainment of gasses while filling of the mold cavity. The majority of the analysis of the casting process has been limited to the metallic casting itself rather than the mold that contains the metal. High-temperature characterization of molding materials has yielded an increased understanding of the condition of the mold and core during solidification. Properties such as thermal expansion, high-temperature reactions, and changes in surface viscosity and decomposition gasses have yielded an increased understanding of the casting process. By using actual high-temperature mechanical property data generated at the foundry, the accuracy of the solidification modeling is improved and the range of capabilities is increased. The use of applied programming interface code can extend the software’s capabilities and yield additional information on the condition of the mold before, during and after solidification. Although once limited in release, new versions of the process modeling software will include the capability to both optimize process variables and develop material-specific datasets that increase both the accuracy and extend the capabilities of the analysis. Using applied programming interface code, the range of capabilities of the process modeling software can be extended to include information on veining defects, final casting dimensions and decomposition gas generation that can result in porosity defects or changes to the thermal properties of the mold.

Growth of Au capped GeO2 nanowires for visible-light photodetection

A single step process to grow Au capped oxygen deficient GeO2 crystalline nanowires via generation of growth species through the metal induced surface decomposition of Ge substrate is reported. Without the external source supply, the growth of the Au-GeO2 nanowires on the Ge substrate is addressed with possible mechanism. Despite high band gap, application of GeO2 as a possible new material for visible light photodetection is presented. The as-grown samples were found to have a photo-response of ≥102 with 17% external quantum efficiency at −2.0 V applied bias upon visible-light illumination (λ = 540 nm, 0.2 mW/cm2). This visible-light detection can be attributed to the oxygen vacancy related defect states as well as localized surface plasmon resonance induced absorption and subsequent hot electron injection from Au to conduction band of GeO2. The photodetection performance of the devices has been understood by the proposed energy band diagrams. In addition, ≈4 times enhancement in the efficiency has been achieved by further decoration of the Au nanoparticles on the as-grown nanowire surfaces.

Gallium Catalysed Direct Growth of Graphene Epitaxial Layer on SiC Substrates By Chemical Vapor Deposition

Graphene, fascinates with its relativistic linear dispersion relation at low energies and the chiral nature of charge carriers, has garnered tremendous interest due to its unusual properties including high electron mobility with low electronic scattering which makes it as a potential candidate in nanoelectronics and photonic devices. Several outstanding advancements in graphene fabrication technology have been explored including research grade mechanical exfoliation of graphite, chemical vapor deposition (CVD), and thermal decomposition of SiC and chemical methods. In particular, the thermal decomposition of SiC surfaces is presently being a very promising approach since it offers wafer scale growth of graphene layers and a promise for high speed nanoelectronics devices. This method utilizes thermal energy to sublimate the topmost Si atoms from the SiC and carbon atoms bond together to form epitaxial graphene. At present, ever growing effort is centered on the direct growth of graphene on SiC substrates by external carbon feedstock using CVD as it would offer several benefits toward the development of wafer scale industrial production of graphene technology on SiC. Moreover, this method facilitates the controlled monolayer growth on the flat SiC surface with high mobility and desirable band gap by varying the mass transport of the carbon precursor. However, a catalytic material must entail to soluble the decomposed carbon atoms on SiC surface to form carbon layers since the underlying SiC shown to have very weak catalytic activity. In this work, we employ a novel approach by utilizing metal gallium vapors as a catalyst and exposing it onto the SiC substrates along the carbon precursor to promote the catalytic activity for the direct fabrication of graphene. At elevated temperatures on the SiC surface, the gallium vapors assist to decompose the acetylene gases and nucleate the carbon atoms to form graphene layers over the substrate scale. The growth mechanism of epitaxial graphene on SiC substrate and the results will be presented in detail.

Electrolyte Systems for High Energy Cells

High energy – high voltage lithium-ion cells are being developed at Argonne as part of the U.S. DOE’s Advanced Battery Research program. These cells typically contain transition-metal bearing layered oxide positive electrodes, graphite-bearing negative electrodes and LiPF6-bearing carbonate solvent electrolytes. Although these cells deliver high energy densities initially, they display significant capacity loss and impedance rise during calendar or cycle-life aging. Extensive diagnostic studies indicate that cell impedance rise mainly arises at the positive electrode, and cell capacity fade mainly results from lithium trapping in the solid electrolyte interphase (SEI) at the negative electrode. During electrochemical aging, both electrodes undergo a cycle of surface film formation, decomposition, dissolution, and redeposition; this process results in continuous consumption of lithium ions, thereby reducing cell capacity and often increasing cell impedance.Electrolyte additives are an economic means of improving cell performance and calendar life. In the past two decades, many organic and inorganic compounds have been identified as effective electrolyte additives: examples include vinylene carbonate, ethylene sulfite, vinyl ethylene carbonate, and fluoroethylene carbonate. However, these additives are mostly used in lithium ion cells that are cycled at relative low voltages (<4.3 V vs Li+/Li). Initial studies indicate that these common electrolyte additives are not effective at enhancing long-term cycling performance of high voltage cells, i.e. stable electrode passivation is not achieved with these traditional additives. Several promising electrolyte additives for high voltage and high capacity lithium-ion cells are being developed at Argonne; these include LiF2BC2O4 (LiDFOB) and various polyfluoroalkyl (PFA) compounds. The PFA additives have two components: (i) a reactive head-group for attachment onto electrode surfaces via either reductive or oxidative decomposition, so that it becomes an integral part of the surface layer; (ii) a polyfluoroalkyl chain that self-assembles on the electrode surface into a solvophobic passivating layer that reduces both surface degradation and electrolyte decomposition. Various additive combinations are also being studied to minimize the performance degradation observed at high voltages. The rationale for electrolyte additive selection and the performance of the resulting electrolyte systems will be highlighted during this presentation.

Formation of Nanoporous Electrode on Aligned CNT Films Using Dealloying

Eco-power systems and recyclable energy are in high demand in low-carbon societies for practical applications of power devices. In these power-device fields, there is a requirement for the development of electronic packages for the radiation of heat. Carbon nanotubes (CNTs) have high thermal conductivities, large electron mean free paths, and large maximum current densities, as compared to metals. For these reasons, the application of CNTs in semiconductor packaging and three-dimensional wires is expected. It is reported that CNTs that have high densities and are well aligned are formed by the surface decomposition of SiC, which is the substrate of the power transistor [1]. However, the contact resistance between the CNTs and the electronic circuit is high. On the other hand, metal nanoparticles have been known to possess various properties that are not present in the bulk and are expected to have applications in various fields such as electronics and biotechnology. Metal nanoparticles have achieved low melting points and high chemical reactivity. Lower temperatures for some processes are expected when using nanosized particles. Au is applied in micro/nano electrochemical systems and in biotechnology applications because it exhibits superior stability and conductivity over other metals. Dealloying is the method used to construct a nanoporous structure by the selective etching of the poor metal from a bimetal consisting of a noble metal and a base metal. We have attempted to form nanoporous structures of Au–Ag films using the electrochemical method and a low-temperature dealloying process [2]. We tried to form metal nanoparticles of Au–Ag on the CNTs to get good contact resistance by dealloying. The purpose of this study is to clarify the initial growth mechanism of the electrodeposited films and nanoporous structures on the aligned CNT films, and to propose an electrode structure with good thermal-emission characteristics.

Laser decontamination and decomposition of PCB-containing paint

Decontamination of concrete surfaces contaminated with paint containing polychlorinated biphenyls is an elaborate and complex task that must be performed within the scope of nuclear power plant dismantling as well as conventional pollutant cleanup in buildings. The state of the art is mechanical decontamination, which generates dust as well as secondary waste and is both dangerous and physically demanding. Moreover, the ablated PCB-containing paint has to be treated in a separate process step.Laser technology offers a multitude of possibilities for contactless surface treatment with no restoring forces and a high potential for automation.An advanced experimental setup was developed for performing standard laser decontamination investigations on PCB-painted concrete surfaces. As tested with epoxy paints, a high-power diode laser with a laser power of 10kW in continuous wave (CW) mode was implemented and resulted in decontamination of the concrete surfaces as well as significant PCB decomposition.The experimental results showed PCB removal of 96.8% from the concrete surface and PCB decomposition of 88.8% in the laser decontamination process. Significant PCDD/F formation was thereby avoided. A surface ablation rate of approx. 7.2m2/h was realized.

ZrB2 thin films deposited on GaN(0001) by magnetron sputtering from a ZrB2 target

ZrB2 films were deposited on 900°C-preheated or non-preheated GaN(0001) surfaces by direct current magnetron sputtering from a compound target. Analytical transmission electron microscopy and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy and electron energy loss spectroscopy revealed a 0001 fiber textured ZrB2 film growth following the formation of a ~2nm thick amorphous BN layer onto the GaN(0001) at a substrate temperature of 900°C. The amorphous BN layer remains when the substrate temperature is lowered to 500°C or when the preheating step is removed from the process and results in the growth of polycrystalline ZrB2 films. The ZrB2 growth phenomena on GaN(0001) is compared to on 4H-SiC(0001), Si(111), and Al2O3(0001) substrates, which yield epitaxial film growth. The decomposition of the GaN surface during vacuum processing during BN interfacial layer formation is found to impede epitaxial growth of ZrB2.

Ohmic Contact for Silicon Carbide by Carbon Nanotubes

The electrical contact properties of silicon carbide (SiC) and carbon nanotubes (CNTs) were measured by conductive atomic force microscopy (C-AFM). A CNT forest was synthesized by SiC surface decomposition. Trenches, which electrically separate the conduction area, were fabricated using a focused ion beam (FIB) without a cover layer, and the resistance of each island was measured by C-AFM. From the dependence of the resistance on the CNT forest island size, the contact resistance between the CNTs and the SiC substrate was measured. By varying the dopant density in the SiC substrate, the Schottky barrier height was evaluated to be ~0.5 eV. This is slightly higher than a previously reported result obtained from a similar setup with a metal covering the CNT forest. We assumed that the damaged region existed in the islands, which is due to the trench formation by the FIB. The commensurate barrier height was obtained with the length of the damaged region assumed to be ~3 μm. Here, we could estimate the resistivity of a CNT/SiC interface without a cover layer. This indicates that a CNT forest on SiC is useful as a brief contact electrode.

Veech surfaces and their periodic points

We give inequalities comparing widths or heights of cylinder decompositions of Veech surfaces with the signatures of their Veech groups. As an application of these inequalities, we estimate the numbers of periodic points of non-arithmetic Veech surfaces. The upper bounds depend only on the topological types of Veech surfaces and the signatures of Veech groups as Fuchsian groups. The upper bounds also estimate the numbers of holomorphic sections of holomorphic families of Riemann surfaces constructed from Veech groups of non-arithmetic Veech surfaces.

Unexpected Li2O2 Film Growth on Carbon Nanotube Electrodes with CeO2 Nanoparticles in Li-O2 Batteries.

In lithium-oxygen (Li-O2) batteries, it is believed that lithium peroxide (Li2O2) electrochemically forms thin films with thicknesses less than 10 nm resulting in capacity restrictions due to limitations in charge transport. Here we show unexpected Li2O2 film growth with thicknesses of ∼60 nm on a three-dimensional carbon nanotube (CNT) electrode incorporated with cerium dioxide (ceria) nanoparticles (CeO2 NPs). The CeO2 NPs favor Li2O2 surface nucleation owing to their strong binding toward reactive oxygen species (e.g., O2 and LiO2). The subsequent film growth results in thicknesses of ∼40 nm (at cutoff potential of 2.2 V vs Li/Li(+)), which further increases up to ∼60 nm with the addition of trace amounts of H2O that enhances the solution free energy. This suggests the involvement of solvated superoxide species (LiO2(sol)) that precipitates on the existing Li2O2 films to form thicker films via disproportionation. By comparing toroidal Li2O2 formed solely from LiO2(sol), the thick Li2O2 films formed from surface-mediated nucleation/thin-film growth following by LiO2(sol) deposition provides the benefits of higher reversibility and rapid surface decomposition during recharge.

Influence of high-temperature processing on the surface properties of bulk AlN substrates

Deep-level luminescence at 3.3eV related to the presence of Al vacancies (VAl) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450°C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H2 and N2 with added NH3. However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH3. Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH3 at temperatures above 1400°C. The surface contamination by Si is thought to generate VAl near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3eV caused by the shallow donor (Si) to VAl transition.

On the Helmholtz Theorem and Its Generalization for Multi-Layers

ABSTRACTThe decomposition of a vector field to its curl-free and divergence-free components in terms of a scalar and a vector potential function, which is also considered as the fundamental theorem of vector analysis, is known as the Helmholtz theorem or decomposition. In the literature, it is mentioned that the theorem was previously presented by Stokes, but it is also mentioned that Stokes did not introduce any scalar and vector potentials in his expressions, which causes a contradiction. Therefore, in this article, Stokes’s and Helmholtz’s representations are examined in detail to reveal and emphasize their differences, similarities and important points. The Helmholtz theorem is obtained for all kinds of spaces by using the theory of distributions in a comprehensive and rigorous manner with detailed explanations, which also leads to a new surface version of the Helmholtz theorem or a new surface decomposition, resulting in the canonical form; hence, it is different than the one suggested previously in terms of two scalar functions. The generalized form of the Helmholtz theorem is also presented by employing the same approach when there is a multi-layer on the surface of discontinuity, which also corresponds to the extension of the theorem to fields with singularities of higher order.

High-Performance Microchanneled Asymmetric Gd(0.1)Ce(0.9)O(1.95-δ)-La(0.6)Sr(0.4)FeO(3-δ)-Based Membranes for Oxygen Separation.

A microchanneled asymmetric dual phase composite membrane of 70 vol % Gd(0.1)Ce(0.9)O(1.95-δ)-30 vol % La(0.6)Sr(0.4)FeO(3-δ) (CGO-LSF) was fabricated by a "one step" phase-inversion tape casting. The sample consists of a thin dense membrane (100 μm) and a porous substrate including "finger-like" microchannels. The oxygen permeation flux through the membrane with and without catalytic surface layers was investigated under a variety of oxygen partial pressure gradients. At 900 °C, the oxygen permeation flux of the bare membrane was 1.6 (STP) ml cm(-2) min(-1) for the air/He-case and 10.10 (STP) ml cm(-2) min(-1) for the air/CO-case. Oxygen flux measurements as well as electrical conductivity relaxation show that the oxygen flux through the bare membrane without catalyst is limited by the oxygen surface exchange. The surface exchange can be enhanced by introduction of catalyst on the membrane surface. An increase of the oxygen flux of ∼1.49 (STP) mL cm(-2) min(-1) at 900 °C was observed when catalyst is added for the air/He-case. Mass transfer polarization through the finger-like support was confirmed to be negligible, which benefits the overall performance. A stable flux of 7.00 (STP) ml cm(-2) min(-1) was observed between air/CO/CO2 over 200 h at 850 °C. Partial surface decomposition was observed on the permeate side exposed to CO, in line with predictions from thermodynamic calculations. In a mixture of CO, CO2, H2, and H2O at similar oxygen activity the material will according to the calculation not decompose. The microchanneled asymmetric CGO-LSF membranes show high oxygen permeability and chemical stability under a range of technologically relevant oxygen potential gradients.

Sampling Based Assessment of the Free-Form Milling Strategies

In this paper, author introduce common needs of increasing surface quality in tool making, a sort of products manufactured by free form milling technology. Principles of the free-form surface decomposition into measurable samples are presented and that is a method of combining CAD modeling with design of sampling objects. Sampling objects are classed both according to their measurability and applied milling strategy. Authors verify experimentally their sampling approach for three milling strategies applied in surface finishing operations while free-form surfaces are investigated in terms of their signed radii. Verification of proposed approach is based on statistical distribution of the measured surface roughness data.