Superstructure Surface Research Articles

Design of a refractive-metasurface hybrid annular aperture folded optical system.

Folded lenses offer advantages in terms of lightness and thinness, but they have limitations when it comes to correcting aberrations. In this paper, we propose a novel approach to address this issue by incorporating metasurfaces in the design of folded optical systems. Specifically, a folded refractive-metasurface hybrid annular aperture folded lens (AFL) is introduced. The structural characteristics of the AFL imaging system are analyzed to investigate the blocking ratio, thickness, and light collection capability of the ring aperture system. Additionally, a hybrid optical integration design using Zemax software is proposed for the metasurfaces. A quadruple-folded AFL working in the mid-infrared waveband is then designed. The superstructure surface is analyzed, and its processability is discussed. The results demonstrate that the reflective-metasurface hybrid AFL significantly improves the imaging quality of this type of optical system while meeting the required design accuracy.

Different Aspect Ratio Polysaccharide-Assisted Assembling of Magnetic Nanoparticles

Versatile methods are here presented for the assembling of magnetic nanoparticles in controlled super-structures with different final aspect ratios. The first step of the procedure is based on the destabilization, and consequently clustering, of a dextran-coated nanoparticles suspension, altering the colloidal stability of the initial building blocks. Subsequently, a second polysaccharide shell, based on chitosan, is grafted to the super-structure surface, for stopping the aggregation of the nanoparticles and enhancing the stability of the resulting assembly. For achieving a finer control of the process, spherical magnetic clusters (SMC) are prepared through a microfluidic aided clustering, investigating the contribution of flow rates and injection scheme geometry to the nanoparticle assembly. Besides, the use of static magnetic fields applied during the first step results in the preparation of micrometric elongated magnetic super-structures (EMS), tuning the average aspect ratio up to a value of 13±4.

Numerical simulation of the impact and freezing stage of supercooled droplets on the ship superstructure surface in the Arctic route

Icing not only affects the stability and safety of Arctic navigation ships but also damages the facilities on board and endangers the safety of personnel. The icing result on the ship’s surface is closely related to the icing process of water droplets on the surface. In the icing process of supercooled water droplets colliding with the ship surface, the impact and icing are coupled with each other. This process is extremely sensitive. The final ice type and physical parameters will change due to the external disturbance. Therefore, in order to obtain accurate ship icing results, the micro impact icing process of water droplets on the surface needs to be considered. From the microscopic point of view, using the numerical simulation method of solidification/melting model in Fluent, this article analyzes the effects of undercooling, contact angle, and droplet impact on the microscopic solidification process of supercooled droplets, and the results show that 1) droplet impact affects the droplet volume; 2) as the impact velocity increases, the freezing time decreases; 3) in the case of the same impact velocity, the freezing time and cooling time vary very closely even if the degree of undercooling and contact angle are different.

Numerical investigation of the impacting and freezing process of a single supercooled water droplet

In order to study the mechanism of ice formation after water droplets produced by splashing waves attach to ship superstructure in cold ocean regions, a numerical framework that considers the effect of supercooling degree on the meso-scale water droplet freezing is developed to explore the freezing mechanism of water droplets after impacting. This model can track the solid–liquid and air–liquid interface together using a coupled volume-of-fluid and level set multiphase method and Enthalpy-Porosity phase change method. The model introduces a mixed fraction to describe the problem of three-phase unification. The simulation results of the center freezing height and droplet spreading factor in this paper are consistent with the experimental results in related literature, which verifies the accuracy of the framework. The study includes a detailed description of the dynamic and thermodynamics mechanism of the water droplet. The influence factors of droplet impacting and freezing process are analyzed. The analysis results show that the surface wettability, supercooling degree, and impact velocity have a great influence on the freezing behavior of droplets. This model can deepen the understanding of icing mechanism on ship superstructure surface, provide an indication for engineers to develop an accurate prediction method of ice accretion on ship superstructure surface.

바람 하중에 의한 크루즈선의 횡경사 예측 및 제어에 관한 연구

The present study considers the prediction of wind-induced heel of cruise ship and its stabilization. Wind load in ocean exerts on the surface of superstructure of cruise ship, which causes the heel moment on the ship. The calculation of wind load starts from choosing wind speed profile, so that the logarithmic wind profile model is applied in this study. Heel moment by wind load is calculated by adopting approximate formulation and applied to the ship motion analysis in time domain. Motion stabilizers, such as stabilizing fin and U-tube tank, are considered to reduce the heel effect as well as excessive roll motion. From this study, it is expected that the present method can be applied to the prediction and stabilization of the heel motion of cruise ships.

Surface electronic bands of submonolayer Ge on Ag(111)

Germanium deposited on single-crystal Ag(111) substrates at about 1/3-monolayer coverage forms a stable $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R{30}^{\ensuremath{\circ}}$ superstructure as seen by reflection high-energy electron diffraction. In situ angle resolved photoelectron spectroscopy reveals a rich band structure consisting of conelike features that cross the Fermi surface at the center ($\overline{\ensuremath{\Gamma}}$ points) of the superstructure surface Brillouin zone (SBZ), exhibiting a high dispersion with the surface parallel wave vector. With the help of first-principles calculations, it can be inferred that most of the features are explained in terms of an Ag${}_{2}$Ge-ordered surface alloy corresponding to surface states localized in the first two layers. One of the bands has a saddle point near the $\overline{\mathrm{M}}$ point of the SBZ with a characteristic split-band behavior distinguishing Ge surface alloy from other similar systems.

Atmospheric pressure oxidation of Pt(111)

The oxidation of the platinum (111) single crystal surface and the formation of platinumdioxide have been studied by in situ surface x-ray diffraction and x-ray reflectivity. At anoxygen partial pressure of 500 mbar and at temperatures from 520 to 910 K, theexperiments disclose the growth of two atomic layers of a bulk-like, strongly distortedα-PtO2.The epitaxial Pt oxide layer is oriented hexagon on hexagon with respect to the Pt(111) surface leadingto a (8 × 8) superstructure surface unit cell. In a second set of experiments, a 100 Å thick epitaxialPt(111) film on sapphire was exposed to oxygen. At 670 K and near atmospheric oxygenpressures we find the formation of a several angstrom thick oxide layer. After annealing thesample at 720 K in a vacuum the oxide layer desorbs, recovering the 100 Å thick Pt film.Subsequent oxidation at 720 K and reduction cycles lead to a slight increase in surfaceroughness and the formation of macroscopically visible holes in the Pt film. These resultspoint to a Pt re-dispersion which sets in during chemical reactions at atmosphericpressures.

He Atomic Beam Scattering Study of Pt(111) Super-Structure Surface Induced by High Energy Molecular Beam of H2O

The super-structure, Pt(111)-(2×2), is investigated both by He atomic beam scattering (HAS) and low energy electron diffraction. The structure is produced by irradiation of a high energy H2O molecular beam, which is accelerated up to about 300 meV by dilution in He gas molecules. The HAS result shows that the structure is stable at 200 K and becomes unstable as the sample temperature is raised to 300 K. The observed structure is believed to be due to reconstruction of the Pt(111) surface, which is caused by H atoms produced during the collision process of H2O molecules with sufficiently high energy for dissociation.

Soliton superlattices on the (0001) surface of C 70 single crystals

Soliton-type superlattices were directly observed on the (0001) face of C 70 single crystals using atomic force microscopy. The images show a stressed surface, with parallel fringes along the 〈2 1 ̄ 0〉 direction, which represent a (p 3 ×1) superstructure, with p=14∼60 in the 〈010〉 direction. Monolayer steps and platelets containing superstructures were also observed on the superstructure surface, consistent with a multilayer reconstruction model. The observed structure also appears to represent a novel example of a one-dimensional sine-Gordon soliton superlattice on the surface of a molecular crystal. The parallel fringes, with a dominant peak-to-peak spacing (half of the full width of the soliton structure) of 27.5±1 nm ( ∼32 3 ×1 superstructure ) and corrugation height difference of 0.3±0.03 nm, were found to be domain walls between face-centered cubic stacking regions and those with hexagonal close-packed stacking on the surfaces of the C 70 single crystals. Molecular resolution images, which were obtained on the surface of the superstructure, support the proposed molecular arrangement model of the soliton superlattice.

Nucleation and surface reconstruction of Pd on Si(100) observed by scanning tunneling microscopy

Abstract The initial stage of crystal growth in the Pd/Si(100) surface for coverages of less than 30 ML (monolayer) was investigated at annealing temperatures between 20°C and 1100°C using STM, LEED, AES and EELS. For deposition at room temperature, the growth mode is of the Volmer-Weber type and small clusters composed of a few atoms nucleate on the substrate Si dimer rows. As temperature increases, small clusters coalesce and these coalesced clusters have a 2 × 2 structure above 800°C. The c(4 × 2) and c(4 × 2) + c(4 × 6) structures appear above 900°C at 1 4 ML and are the same as those of the Pt/Si(100) surface. For coverages higher than 1 4 ML, excess Pd atoms form silicide (PdSi) islands on the superstructure surface in the Stranski-Krastanov mode. The electronic structure of the Pt/Si(100) surface depending on the coverage and annealing temperature is discussed from the AES and EELS data.

Nucleation and surface reconstruction of Pd on Si(100) observed by scanning tunneling microscopy

The initial stage of crystal growth in the Pd/Si(100) surface for coverages of less than 30 ML (monolayer) was investigated at annealing temperatures between 20°C and 1100°C using STM, LEED, AES and EELS. For deposition at room temperature, the growth mode is of the Volmer-Weber type and small clusters composed of a few atoms nucleate on the substrate Si dimer rows. As temperature increases, small clusters coalesce and these coalesced clusters have a 2 × 2 structure above 800°C. The c(4 × 2) and c(4 × 2) + c(4 × 6) structures appear above 900°C at 1 4 ML and are the same as those of the Pt/Si(100) surface. For coverages higher than 1 4 ML, excess Pd atoms form silicide (PdSi) islands on the superstructure surface in the Stranski-Krastanov mode. The electronic structure of the Pt/Si(100) surface depending on the coverage and annealing temperature is discussed from the AES and EELS data.

Phase transitions on reconstructed (110) surfaces

The deconstruction transition of the (110) surface of Au and Pt is investigated theoretically. A previous treatment by the same authors is first revisited in the light of recent experiments. Then, a more refined model, based on the transfer matrix formalism, is introduced, which takes into account short-range interaction between steps. For strong attractive interaction a pair of opposite steps is bound to form an Ising domain wall and the system undergoes, upon heating, first an Ising transition and at higher temperature, when the steps unbind, a roughening transition. For weak or repulsive interaction between the opposite steps, when the pair is not bound, a roughening and deconstruction transitions are expected to occur at the same temperature. The Ising and the two roughening transitions merge in the multicritical point. The shift of the superstructure surface peak above the transition is investigated. The ratio shift/width is found to vanish at the transition for an Ising transition, in contrast with experiments on Pt. It is argued that the actual Au and Pt surface phase transitions are very close to the multicritical point.

Phase transitions on reconstructed (110) surfaces

Abstract The deconstruction transition of the (110) surface of Au and Pt is investigated theoretically. A previous treatment by the same authors is first revisited in the light of recent experiments. Then, a more refined model, based on the transfer matrix formalism, is introduced, which takes into account short-range interaction between steps. For strong attractive interaction a pair of opposite steps is bound to form an Ising domain wall and the system undergoes, upon heating, first an Ising transition and at higher temperature, when the steps unbind, a roughening transition. For weak or repulsive interaction between the opposite steps, when the pair is not bound, a roughening and deconstruction transitions are expected to occur at the same temperature. The Ising and the two roughening transitions merge in the multicritical point. The shift of the superstructure surface peak above the transition is investigated. The ratio shift/width is found to vanish at the transition for an Ising transition, in contrast with experiments on Pt. It is argued that the actual Au and Pt surface phase transitions are very close to the multicritical point.