Vacuum Layer Research Articles

Dewetting during Terahertz Vibrations of Nanoparticles

We use molecular simulations to demonstrate the formation of a vacuum layer around a vibrating nanoparticle in a liquid. This vacuum layer forms readily for high frequencies with respect to the characteristic vibrational (Einstein) frequency of the fluid, even with small amplitude vibrations. The opposite is true for low frequencies, where large amplitudes are required to demonstrate the vacuum layer. With the vacuum layer forming, the quality factor of the oscillations increases substantially. The findings provide an interpretation of our recent experiments that show the onset of high-quality resonances of nanoparticles in water ( Xiang et al. Nano Lett. 2016 , 16 , 3638 ) in the gigahertz to terahertz range.

Method for Reducing Outgas from Materials Used at the Vacuum Layer in Cryogenic Vessels and Its Evaluation

Method for Reducing Outgas from Materials Used at the Vacuum Layer in Cryogenic Vessels and Its Evaluation

Development of Numerical Heat Transfer and the Structural Model to Design Slim and Translucent Vacuum Layer Type Insulation Panels to Retrofitting Insulation in Existing Buildings

The authors develop slim and light-weight vacuum insulation panels (VIPs) by producing vacuum layers with spacers and plastic plates. The developed VIPs have the advantages of a low cost and easy installation, thus facilitating retrofitting insulation of existing buildings. In addition, one of the developed VIPs is slim and translucent so it can be easily used for windows in an internal installation. In this paper, the authors first propose a vacuum layer type slim translucent VIP and focus on a reasonable design method. Next, the authors introduce the design process in which the structural design is obtained with element mechanical analysis and a three-dimensional analysis is conducted for the VIP element. In the study, a heat transfer model is used to predict the insulation performance through finite element analysis (FEA). Subsequently, the authors perform an experiment to measure the thermal conductivity in a guarded hot plate apparatus to validate the performance prediction. Finally, case studies are performed to confirm how the different design conditions affect the insulation performance. The optimum design of the vacuum layer type slim and translucent VIP will have a sufficient structural strength to hold and maintain the vacuum layer. The thermal conductivity is approximately 0.007 W / ( m · K ) , which can effectively improve the insulation performance in applications.

Oxygen Reduction Reaction Catalytic Sites on Carbon-Coated Fe3C Catalyst

Proton-exchange membrane fuel cells (PEMFC) are promising chemical-to-electrical energy conversion devices which can potentially replace combustion engine in automobiles. Their commercialization is currently suppressed primarily due to the price of the platinum catalyst for the cathodic oxygen reduction reaction (ORR). Required platinum loading per fuel-cell car is about 10 times higher than for the conventional one [1], which results in a significant contribution to the car price. Therefore, either the platinum loading needs to be drastically decreased, or a stable and active non-precious metal catalyst has to be developed. Recently, a new type of ORR catalyst composed of carbon-coated iron carbide nanoparticles has been synthesized [2]. It exhibits only slightly lower activity than, and comparable durability to platinum in acidic solutions. It has been suggested that a new ORR catalytic site may have been discovered [3]. In this work we study the catalyst by means of the Density Functional Theory to identify its active sites. Spin-polarized DFT calculations are performed using the Vienna Ab Initio Simulation Package (VASP) with PAW potentials, BEEF-vdW exchange-correlation functional [4], plane wave cutoff of 400 eV and vacuum layer of 14 Å. The model system consists of Fe3C/carbon interface and a few explicit water molecules to model the liquid environment. The following factors influencing the activity are taken into account: (i) thickness of the carbon layer (single- or multilayer graphene), (ii) defects in the carbon structure, (iii) nitrogen doping, (iv) adsorbate coverage, (v) presence of spectator adsorbates. A few other catalyst structures, which are independent of the presence of iron carbide, but still may exist in the real system, are also studied. These include catalysts with porphyrin-iron moiety embedded in the graphene structure and defective graphene with or without nitrogen doping. As a result, a few possible structures of catalytic sites in the carbon-coated Fe3C catalyst are proposed. [1] H.A. Gasteiger, D.R. Baker, R.N. Carter, W. Gu, Y. Liu, F.T. Wagner, P.T. Yu, in Hydrogen and Fuel Cells: Fundamentals, Technologies and Applications (D. Stolten, Ed.) Ch. 1 p. 3, Wiley-VCH, Weinheim, 2010. [2] Y. Hu, J. O. Jensen, W. Zhang, L. N. Cleemann, W. Xing, N. J. Bjerrum, Q. Li, Angew. Chem. Int. Ed., 2014, 53, 3675. [3] J.-P. Dodelet, R. Chenitz, L. Yang, M. Lefèvre, ChemCatChem, 2014, 6, 1866. [4] J. Wellendorff, K.T. Lundgaard, A. Møgelhøj, V. Petzold, D.D. Landis, J.K. Nørskov, T. Bligaard, K.W. Jacobsen, Phys. Rev. B, 2012, 85, 235149.

Energy Performance Assessment of a 2nd-Generation Vacuum Double Glazing Depending on Vacuum Layer Position and Building Type in South Korea

(1) Background: The application of high insulation to a building envelope helps reduce the heating load, but increases the cooling load. Evaluating the installation of high insulation glazing to buildings in climate zones with four distinct seasons, as in the case of South Korea, is very important; (2) Methods: This study compared the heating energy performance of four types of glazing, inside vacuum double glazing, outside vacuum double glazing, single vacuum glazing, and low-e double glazing, with fixed low-e coating positions on the inside of the room in a mock-up chamber under the same conditions. The annual energy consumption according to the building type was analyzed using a simulation; (3) Results: As the insulation performance of building envelopes has increased, the energy saving rate of inside vacuum double glazing has been increased further in office buildings. In residential buildings, the energy saving rate of inside vacuum double glazing with a low SHGC (solar heat gain coefficient) has become higher than that of outside vacuum double glazing; (4) Conclusions: Since the effects of SHGC on the energy saving rates are greater in high insulation buildings, SHGC should be considered carefully when selecting glazing in climate zones with distinct winter and summer seasons.

Radiation of Heat in an Insulating Vacuum Layer

Abstract The paper is motivated by the previous research concerning the heat transfer in a heat accumulation device. The device had been explored, built up and tested with the aim of utilization of cheap solar energy and its storage. In this heat storage system, a vacuum-like gap between two concentric containers acts as an insulating layer, radiation being the predominant heat transfer type in the gap. The better knowledge and understanding of the heat exchange by radiation, the more effectiveness of the insulation of the layer can be reached. Heat transfer by radiation is explored in the paper, mathematical model is set up, the algorithm of non-linear transient computation is introduced, and some illustrative results of this computation are performed.

Asymptotic approximations for the stationary radiative-conductive heat transfer problem in the two-dimensional system of plates

Abstract Special asymptotic approximations, namely, the first and second homogenized problems are proposed for the boundary value problem describing a stationary radiative-conductive heat transfer in a two-dimensional system of heat-conducting plates of thickness ɛ separated by vacuum layers. The unique solvability of homogenized problems is proved, the comparison theorem is established, and estimates of solutions are obtained. The first homogenized problem has the error estimate of order O ( ε ) $ O(\sqrt{\varepsilon}) $ .

Band offsets of Ag2ZnSnSe4/CdS heterojunction: An experimental and first-principles study

Band offsets at the interface of the Ag2ZnSnSe4 (AZTSe)/CdS heterojunction were systematically investigated by combining experiments and first-principles calculations. For the AZTSe/CdS interface, a higher conduction-band minimum (CBM) of the CdS than that of the AZTSe was found and the conduction-band offset of 0.31 eV was determined using X-ray photoelectron spectroscopy. Theoretically, we constructed the AZTSe/CdS interface and calculated the band alignments. Two different configurations were adopted in the calculations: the AZTSe/CdS superlattice and the AZTSe/CdS heterojunction with a vacuum layer. The calculated results indicate that CdS has a higher CBM than AZTSe at the AZTSe/CdS interface, well supporting the experimental results. Our results suggest that the AZTSe/CdS heterojunction has an ideal band structure for photovoltaic applications.

Thermal analysis of walls in a new-type billet caster tundish with a vacuum shell

To reduce thermal loss from molten steel in a tundish during continuous casting production, a new tundish fabricated by welding radiation-proof steel plates onto the steel plates of the exterior walls of a billet caster tundish was proposed. This new tundish was used to investigate the effect of pressures inside the vacuum chamber on the uniformity of the temperature of molten steel and the thermal conditions of the vacuum layer. The results show that the conversion radiation coefficient is not sensitive to pressure and its value at high temperatures is merely 1.5 times greater than that at low temperatures. Pressure is the key factor affecting additional factor of conversion convection. This factor is more than 100 times greater at 105 Pa than at 102 Pa, and the temperature at inner points at 102 Pa is, on average, 4 K higher than that at 105 Pa. Meanwhile, the local temperature difference of the inlet at 102 Pa is 1 K higher than that at 105 Pa. Thus, the proposed vacuum billet caster tundish can achieve low superheat teeming of steel because of the thermal preservation capability of the vacuum, which helps to reduce the tapping temperature and improve the uniformity of the temperature of steel.

Performance of a Depleted Uranium Bed for a Nuclear Fusion Fuel Cycle

The Tritium Storage & Delivery System (SDS) is part of a tokamak-type nuclear fusion reactor fuel cycle. For the safety of this cycle, the hydrogen isotopes are stored in a metal hydride form in the SDS. Depleted uranium (DU) was chosen as the storage material. DU hydride can be heated to very high temperatures that are sufficient for pumping hydrogen isotopes without using gas pumps. The experimental apparatus used to test the experimental DU bed consists of a tank that stores and measures the hydrogen, and a DU bed used for the hydriding and dehydriding of hydrogen. The DU bed is a vertical double-cylinder type with sintered metal filters. The bed is composed of primary and secondary vessels. The primary vessel contains DU, and a vacuum layer is formed between the primary and secondary vessels. In this study, recent experimental results on the pretreatment (activation and powderization) of DU and the direct hydrogen recovery and delivery of a DU bed are presented. In addition, the relationship between hydrogen pressure and temperature in the DU bed is obtained.

Steering air bubbles with an add-on vacuum layer for biopolymer membrane biofabrication in PDMS microfluidics.

Membrane functionality is crucial in microfluidics for realizing operations such as filtration, separation, concentration, signaling among cells and gradient generation. Currently, common methods often sandwich commercially available membranes in multi-layer devices, or use photopolymerization or temperature-induced gelation to fabricate membrane structures in one-layer devices. Biofabrication offers an alternative to forming membrane structures with biomimetic materials and mechanisms in mild conditions. We have recently developed a biofabrication strategy to form parallel biopolymer membranes in gas-permeable polydimethylsiloxane (PDMS) microfluidic devices, which used positive pressure to dissipate air bubbles through PDMS to initiate membrane formation but required careful pressure balancing between two flows. Here, we report a technical innovation by simply placing as needed an add-on PDMS vacuum layer on PDMS microfluidic devices to dissipate air bubbles and guide the biofabrication of biopolymer membranes. Vacuuming through PDMS was simply achieved by either withdrawing a syringe or releasing a squeezed nasal aspirator. Upon vacuuming, air bubbles dissipated within minutes, membranes were effortlessly formed, and the add-on vacuum layer can be removed. Subsequent membrane growth could be robustly controlled with the flows and pH of solutions. This new process is user-friendly and has achieved a 100% success rate in more than 200 trials in membrane biofabrication.

Temporal differentiation and integration of 3D optical pulses using phase-shifted Bragg gratings

We consider diffraction of a three-dimensional (3D) spatiotemporal optical pulse by a phase-shifted Bragg grating (PSBG). The pulse diffraction is described in terms of signal propagation through a linear system with its transfer function determined by the reflection or transmission coefficient of the PSBG. It is shown that a PSBG can perform temporal differentiation in reflection and temporal integration in transmission of a 3D spatiotemporal optical pulse envelope. Second order differentiation of the incident pulse envelope is achieved using two differentiating PSBGs separated by a vacuum layer with the optical thickness of a quarter of the Bragg wavelength. The possibility of performing the said operations are confirmed by rigorous simulation results.

Structure of NO dimer multilayer on Rh(111)

Molecular self-assembly is the spontaneous organization of molecules under thermodynamic equilibrium conditions into well-defined arrangements via cooperative effects between chemical bonds and weak noncovalent interactions. Molecules undergo self-association without external instruction to form hierarchical structures. Molecular self-assembly is ubiquitous in nature and has recently emerged as a new strategy in chemical biosynthesis, polymer science and engineering. NO monomer is apt to be absorbed on the surfaces of some metals such as Ir(111), Ni(111), Pd(111), Pt(111), Rh(111) and Au(111), and the interactions of NO monomer with the metal surfaces have been extensively studied. When NO monomer is weakly adsorbed on the noble-metal surface, it cannot be reduced completely but forms a stable structure, which is named NO dimer. The first-principle technique is employed to determine the structures of NO dimer ((NO)2) molecular chains and monolayers on virtual Rh(111), as well as (NO)2 monolayer and multilayer on Rh(111). First, (NO)2 monomers are assembled into two stable molecular chains on the virtual Rh(111) surface, whose bind energies are 0.309 and 0.266 eV, respectively. The molecular chains are self-assembly systems, in which (NO)2 monomers are parallel and ordered, and the O atoms and N atoms are shown to be of (100) and (111) structures, respectively. Then, the two molecular chains are assembled into two stable monolayers (denoted as M1 and M2) on the virtual Rh(111)-(13), and the coverage is 1.00 ML. In the M1 monolayer, the angle between the NN bond of (NO)2 monomer and the substrate is in a range of 70-90, and in the M2 monolayer, the NN bond is parallel to the substrate.In the adsorption system of M2/Rh(111), (NO)2 molecules can be adsorbed on the top as well as the hcp and fcc hollow sites. When (NO)2 molecules are adsorbed on the top site, the adsorption system is best described by the electron structure Rh+0.14N0=O-0.14, and when (NO)2 molecules are absorbed on the two hollow sites, the adsorption system is described by the electron structure Rh+0.34N-0.18=O-0.16. Therefore, (NO)2 molecules are more apt to be adsorbed on the two hollow sites than on the top site. In the adsorption systems of M1+M2/Rh(111) and M1+(M1+M2)/Rh(111), (NO)2 molecules are adsorbed vertically on the two hollow sites, the NN bond is parallel to the substrate in the first monolayer, and the angle between the NN bond and the substrate is in a range of 70-90 in the second and third monolayers. The interaction between the neighbor monolayers is about 0.01 eV, and the thickness of the vacuum layer is 0.31 nm0.02 nm.

Finite field methods for the supercell modeling of charged insulator/electrolyte interfaces

Interactions between aligned dipoles in periodic model systems are often considered spurious and removed by partitioning the supercell in isolated slabs separated by vacuum layers. One popular and efficient screening approach is the so-called dipole correction. In this work, the authors present an alternative finite-field based method which retains all electrostatic interactions and dispenses with vacuum layers. Adapting the constant-$D$ approach developed by Stengel, Spaldin, and Vanderbilt for the study of ferroelectric nanocapacitors, the new scheme here is intended for molecular dynamics simulations of the interface between an insulator carrying a specifically absorbed surface charge and an ionic conductor (the electrolyte) at finite temperature. The authors show that the dipole correction scheme is equivalent to $D$=0 electric boundary conditions with or without vacuum layers. Thus, both global polarization $P$ of the heterogeneous system and corresponding average macroscopic electric field $E$ are finite. The authors then continue with the investigation of the variation of $P$ with $E$ or $D$ and validate expressions based on $P$ for computing the electric double-layer capacitance using atomistic simulations.

Three-layer model for the surface second-harmonic generation yield including multiple reflections

We present the three-layer model to calculate the surface second-harmonic generation (SSHG) yield. This model considers that the surface is represented by three regions or layers. The first layer is the vacuum region with a dielectric function ${\ensuremath{\epsilon}}_{v}(\ensuremath{\omega})=1$ from where the fundamental electric field impinges on the material. The second layer is a thin layer $(\ensuremath{\ell})$ of thickness $d$ characterized by a dielectric function ${\ensuremath{\epsilon}}_{\ensuremath{\ell}}(\ensuremath{\omega})$, and it is in this layer where the SSHG takes place. The third layer is the bulk region denoted by $b$ and characterized by ${\ensuremath{\epsilon}}_{b}(\ensuremath{\omega})$. Both the vacuum and bulk layers are semi-infinite. The model includes the multiple reflections of both the fundamental and the second-harmonic (SH) fields that take place at the thin layer $\ensuremath{\ell}$. We obtain explicit expressions for the SSHG yield for the commonly used $s$ and $p$ polarizations of the incoming $1\ensuremath{\omega}$ and outgoing $2\ensuremath{\omega}$ electric fields, where no assumptions for the symmetry of the surface are made. These symmetry assumptions ultimately determine which components of the surface nonlinear second-order susceptibility tensor $\mathbf{\ensuremath{\chi}}(\ensuremath{-}2\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega})$ are different from zero, and thus contribute to the SSHG yield. Then, we particularize the results for the most commonly investigated surfaces, the (001), (110), and (111) crystallographic faces, taking their symmetries into account. We use the three-layer model and compare it against the experimental results of a Si(111)$(1\ifmmode\times\else\texttimes\fi{}1)$:H surface, as a test case, and use it to predict the SSHG yield of a Si(001)$(2\ifmmode\times\else\texttimes\fi{}1)$ surface.

New insight into investigation of thermal transfer of molten steel inside a ladle with vacuum shell

In order to reduce the amount of thermal loss of steel inside a ladle during the industrial production, one new type ladle constructed using radiation-proof steel plates welded on the exterior walls of conventional ladle and its lid was investigated. Thermal insulation principle of vacuum is applied to study the mechanism of thermal transfer, and a novel approach is proposed for calculation of comprehensive thermal conductivity inside the vacuum chamber. The main idea of this paper was to explore the effects of pressures inside vacuum chamber on the temperature of molten steel. The conclusions were made. When the absolute pressure inside the chamber of the ladle is set to 50 Pa, as with its lid, the temperature drop of molten steel is a mere 9 K; while the chamber of the ladle is set to 105 Pa, as with its lid, the temperature drop is 37 K and heat flux occupies the minimum proportion value, 15.38 %. Thermal conduction ability of air molecule is almost not affected by pressure. The additional conversion convection factor value at 104 Pa is 200 times larger than that at 50 Pa. The ability of comprehensive thermal conduction is poor due to low pressures and small amount of air molecules. Thermal conductivity of refractory layer is 11 times larger than that of vacuum layer at 50 Pa. Thus, vacuum layer has strong thermal insulation at lower vacuum pressures.

(Invited) First-Principles Simulations of Electrochemical Reactions and Properties at Water|Pt Interfaces

A first step for understanding the electrochemical reactions from fundamental point of view is ab-initio calculations to find the reaction path and the energy profile along the reaction cooprdinate. More reliable and more realistic way including solvent, temperature, electrolyte, electrode interface, etc., is to use first-principles molecular dynamics. A pioneer work in this direction is that by Ishiwaka and co-workers [1]. They used a cluster Pt with water molecules. They followed the first step of the hydrogen evolution, i.e. H adsorption on Pt. They controlled the electrode potential by changing the number of electrons in the system. We used the slab model under the periodic boundary conditions [2]. Electrode potential was controlled by using the effective screening medium (ESM) [3] separated from the water layer on Pt with a vacuum layer. Hydrogen adsorption from H3O+was observed with a charge transfer between Pt layer and the hydronium ion. Water structure on Pt is important properties to understand fuel cell reactions and H2/O2 evolution from water by electrochemical reactions [6-11]. H-down adsorption structure of water molecules with well-developed hydrogen network with H3O+ was observed on Pt(111) surface. O-H stretching vibrations of H2O on Pt was in a function of the electrode potential. Specific adsorption on Pt electrode is also an important factor in the electrochemical reaction on it. SO4 2– and HSO4 –adsorptions were observed on the potential controlled Pt [12,13]. Vibration properties of adsorbed (bi)sulfate on the Pt(111) surface were obtained by FPMD with the cluster and slab models. Our work shown here has been performed with collaboration among M. Otani (AIST), I. Hamada (NIMS), O. Sugino (Univ. Tokyo), Y. Morikawa (Osaka Univ.), Y. Okamoto (NEC), and Y. Qian (FC-Cubic). [1] Y. Ishikawa, J. J. Mateo, D. A. Tryk, and C. R. Cabrera: J. Electroanal. Chem. 607, 37 (2007). [2] J. A. Santana, J. J. Mateo, and Y. Ishikawa, J. Electroanal. Chem. 607, 37 (2007). [3] M. Otani and O. Sugino, Phys. Rev. B 73, 115407 (2006). [4] O. Sugino, I. Hamada, M. Otani, Y. Morikawa, T. Ikeshoji, and Y. Okamoto, Surf. Sci. 601, 5237 (2007). [5] M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, and T. Ikeshoji, J. Phys. Soc. Jpn. 77, 024802 (2008). [6] Y. Ishikawa, J. J. Mateo, D. A. Tryk, and C. R. Cabrera, J. Phys. Chem. C 114, 4995–5002 (2010). [7] J. A. Santana, C. R. Cabrera, Y. Ishikawa, Phys. Chem. Chem. Phys. 12, 9526 – 9534 (2010). [8] M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, and T. Ikeshoji Phys. Chem. Chem. Phys. 10, 3609- 3612 (2008). [9] T. Ikeshoji, M. Otani, I. Hamada, and Y. Okamoto, Phys. Chem. Chem. Phys., 13, 20223-20227 (2011). [10] T. Ikeshoji, M. Otani, I. Hamada, O. Sugino, Y. Morikawa, Y. Okamoto, Y. Qian, and I. Yagi, AIP Adv. 2, 032182 (2012). [11] Y. Qian, I. Hamada, M. Otani, and T. Ikeshoji, Catal. Today 202, 163-167 (2013). [12] J. A. Santana, C. R. Cabrera, Y. Ishikawa, Phys. Chem. Chem. Phys. 12, 9526 – 9534 (2010). [13] Y. Qian, T. Ikeshoji, Y. Zhao, and M. Otani, ChemElectroChem 1, 1632-1635 (2014).

Local Structural Distortion Induced Uniaxial Negative Thermal Expansion in Nanosized Semimetal Bismuth.

The corrugated layer structure bismuth has been successfully tailored into negative thermal expansion along c axis by size effect. Pair distribution function and extended X-ray absorption fine structure are combined to reveal the local structural distortion for nanosized bismuth. The comprehensive method to identify the local structure of nanomaterials can benefit the regulating and controlling of thermal expansion in nanodivices.

Measurement of effective sheath width around the cutoff probe based on electromagnetic simulation

We inferred the effective sheath width using the cutoff probe and incorporating a full-wave three-dimensional electromagnetic (EM) simulation. The EM simulation reproduced the experimentally obtained plasma-sheath resonance (PSR) on the microwave transmission (S21) spectrum well. The PSR frequency has a one-to-one correspondence with the width of the vacuum layer assumed to be the effective sheath in the EM simulation model. The sheath width was estimated by matching the S21 spectra of the experiment and the EM simulation for different widths of the sheath. We found that the inferred sheath widths quantitatively and qualitatively agree with the sheath width measured by incorporating an equivalent circuit model. These results demonstrate the excellent potential of the cutoff probe for inferring the effective sheath width from its experimental spectrum data.

Large Spatial Spin Polarization at Benzene/La2/3Sr1/3MnO3 Spinterface: Toward Organic Spintronic Devices

The fascinating spinterfaces between benzene and La2/3Sr1/3MnO3 (LSMO) are investigated based on the first-principles calculations. LSMO is a traditional high spin-polarized material used as the electrode in organic spintronic devices. However, the understanding of spin characteristics at organic/LSMO interfaces is unclear. Therefore, we study the benzene/LSMO spinterfaces to clarify the spin behaviors at organic/LSMO interfaces because benzene is the basic unit of organic molecules. It is found that SrO terminations have weak binding with benzene, showing the inert properties. More importantly, the positive spatial spin polarization expands into the benzene layer and vacuum layer in all of the models. To further make sure the credibility of the results, both the effect of the ordering of Sr atoms and the adsorption density of benzene are considered in our calculations. There is no spatial spin-polarization inversion above the benzene plane in all of the models. The results indicate that the organic layer...