Hexagonal Surface Structure Research Articles

Water-Etched Porous Ti: Surface Manipulation of Ti Foam Fabricated by Liquid Metal Dealloying Technique.

The liquid metal dealloying (LMD) process enables the fabrication of porous metals with various chemical compositions. Despite its advantages, LMD still faces key challenges such as maintaining the high-temperature molten metal bath for a prolonged time, avoiding the use of toxic etchants, and so on. To overcome these challenges, the study develops a water-leachable and oxidation-resistant alloy melt (AM) in Ca-Mg binary system. Specifically, Ca72Mg28 eutectic AM is designed, which exhibits higher oxidation resistance and lower melting temperature compared to pure Mg, allowing LMD to be conducted in atmospheric conditions as well as temperatures >200K lower. The AM also enables an innovative process to fabricate Ti foams with a hexagonal faceted surface structure by carefully manipulating the etching rate during the water etching process. This approach allows for the creation of foam with a surface area over 13% larger than that of foams with smooth surfaces via normal acid etching, potentially enhancing efficiency in applications such as electrodes for electrochemical systems or biomedical materials where increased cell adhesion can be beneficial. This study paves the way for efficiently manipulating the LMD process to fabricate metal foams with customized compositions and enhanced surface properties.

Characterization and Adsorption Capacity Evaluation of ZnCl2 Impregnated Cassava Peel Carbon for Removal of Fe, Ca, Mg and Zn ions in Wastewater from Cassava processing Industry

The objective of this paper was to prepare, characterize and evaluate the adsorption capacity of cassava peel carbon (CPC) impregnation with ZnCl2 salt for the removal of Fe, Ca, Mg and Zn ions in wastewater derived from cassava processing which has been noted to be problematic in terms of management. CPC and cassava peel activated carbon (CPAC) at 1:3, 2:3, and 1:1 impregnation levels were placed in fixed bed adsorption columns to determine metal ion adsorption capacities of the carbon materials after 120, 240, 360 and 480-minute contact times. Langmuir and Freundlich isotherm models were used in assessment of adsorption of the carbon materials, while pseudo-first and second order models were used to validate the adsorption kinetics of Fe, Ca, Mg and Zn. Pore space development was also monitored using scanning electron microscope (SEM) imagery. Results SEM images revealed hexagonal honeycomb surface structure at 2:3 impregnation level and spongy configuration at 1:1 ZnCl2 impregnation level. The correlation coefficient of Langmuir isotherm was observed to be between 0.86 to 1, indicating that the adsorbent is very good in adsorption of the metals, however, Freundlich isotherm is found to be unfavorable in describing CPAC’s capacity in adsorbing zinc ion contaminant. The pH of the carbon materials was observed to have increased while the bulk density reduced with increasing level of impregnation. Conclusively, CPC and CPAC materials are well suited to Langmuir isotherm as well as pseudo-second order model, implying that adsorption occurs well in a monolayer form on the surface material surface.

Accommodating a hexagonal [formula omitted]- phase Mn2N film on a cubic MgO (001) substrate

The thin films of c-plane dominated hexagonal ζ- phase Mn2N were successfully grown on a cubic MgO (001) substrate directly using plasma-assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo-cubic domains along [100]MgO and [110]MgO, and one hexagonal domain, which is 30° apart from the [100]MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 × 2 reconstructed surface is presented. For the c-plane surface, theoretical investigations were carried out using first-principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows that the nitrogen terminated 2 × 2 structure with a manganese adatom on the surface is the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed in-plane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1.

Low optical diffraction random hexagonal structure metallic network conductive films

Traditional metallic meshes are a two-dimensional square structure with high optical transmittance loss, and the diffraction of light seriously interferes with the imaging quality of the detection system. In this work a metallic network conductive film with a random hexagonal surface structure is designed. This structure has a higher optical transmittance than conventional square metallic meshes. As a result of the random variables in the structure, it can also suppress the stray light of high-order diffraction. Then we prepare a metallic network conductive film on a ZnS optical window with a line width of 4 μm and a period of 100 μm. The metal lines of the sample are clear, the line width is uniform, and there is no dotted line. The transmission loss of the ZnS optical window is 10.5% in the long-wave infrared band (LWIR) band but only 6.8% in the visible band, which has low energy loss. At the same time, it can achieve uniform optical diffraction, thus reducing the imaging interference to the photoelectric detection system. The numerical simulation results show that the average EMI shielding efficiency is 37.9db, which is in an electromagnetic spectrum range from 0.2 GHz to 20 GHz, and its minimum shielding efficiency is 29.6 dB, which is 3.2 dB higher than the traditional square mesh’s. The random hexagonal structure metallic network conductive films designed and prepared in this paper have excellent optical properties and EMI shielding efficiencies, which is of great significance in improving the comprehensive performance of the graphical optical window.

Synthesized 2nd Generation Zeolite as an Acid-Catalyst for Esterification Reaction

MCM-48 zeolites have unique properties from the surfaces and structure point of view as it’s shown in the results ,and unique and very sensitive to be prepared, have been experimentally prepared and utilized as a second-generation/ acid - catalyst for esterification reactions of oleic acid as a model oil for a free fatty acid source with Ethanol. The characterization of the catalyst used in the reaction has been identified by various methods indicating the prepared MCM-48 is highly matching the profile of common commercial MCM-48 zeolite. The XRF results show domination of SiO2 on the chemical structure with 99.1% and agreeable with the expected from MCM-48 for it's of silica-based, and the SEM results show the cubic crystallographic space group compatible with Ia3d space group giving the hexagonal surface structure. The AFM test gave an average particle diameter of 97.51 nm and an average catalyst roughness of 0.855 nm. Esterification reaction of oleic acid with ethanol on MCM-48 has been carried in a batch reactor with 5% the prepared MCM-48 zeolite catalyst loading gives 81% of conversion after one hour at 353K

Coverage and Stability of NHx-Terminated Cobalt and Ruthenium Surfaces: A First-Principles Investigation

In the atomic layer deposition (ALD) of cobalt (Co) and ruthenium (Ru) metals using nitrogen plasma, the structure and composition of the post N-plasma NHx-terminated (x = 1 or 2) metal surfaces are not well-known but are important in the subsequent metal-containing pulse. In this paper, we use the low-index (001) and (100) surfaces of Co and Ru as models of the metal polycrystalline thin films. The (001) surface with a hexagonal surface structure is the most stable surface, and the (100) surface with a zigzag structure is the least stable surface but has high reactivity. We investigate the stability of NH and NH2 terminations on these surfaces to determine the saturation coverage of NHx on Co and Ru. NH is most stable in the hollow hexagonal close-packed site on the (001) surface and the bridge site on the (100) surface, while NH2 prefers the bridge site on both (001) and (100) surfaces. The differential energy is calculated to find the saturation coverage of NH and NH2. We also present results on mixed ...

Growth of graphene monolayer by “internal solid-state carbon source”: Electronic structure, morphology and Au intercalation

Synthesis of a graphene monolayer atop Ni(111) film deposited on HOPG using method of “internal solid-state carbon source” due to low-temperature segregation of carbon atoms through Ni film from the Ni/HOPG interface was studied by core level and valence band photoelectron spectroscopy. The atomic structure and morphology were studied by STM. It was established that the synthesis of graphene occurs via a stage of transformation from the surface carbide phase (with stoichiometry Ni2C) as a result of the surface carbide decomposition. We consider that such transformation is a necessary stage of the graphene synthesis. We have shown that the method of “solid-state carbon source” indeed results in a graphene monolayer formation on top of Ni film. A graphene monolayer begins to form even under annealing at 180°C. Formation of practically full graphene covering with well-ordered structure takes place even at temperature of 260–270°C. The formed graphene is strongly coupled to the Ni substrate. STM images show formation of well-ordered atomic hexagonal surface structure characteristic for graphene monolayer. Intercalation of Au atoms leads to formation of the p(9×9) superstructure and blocks strong coupling. It testifies that the main part of the surface is covered by epitaxial graphene on Ni.

Band-gap engineering by Bi intercalation of graphene on Ir(111)

We report on the structural and electronic properties of a single bismuth layer intercalated underneath a graphene layer grown on an Ir(111) single crystal. Scanning tunneling microscopy (STM) reveals a hexagonal surface structure and a dislocation network upon Bi intercalation, which we attribute to a $\sqrt{3}\times\sqrt{3}R30{\deg}$ Bi structure on the underlying Ir(111) surface. Ab-initio calculations show that this Bi structure is the most energetically favorable, and also illustrate that STM measurements are most sensitive to C atoms in close proximity to intercalated Bi atoms. Additionally, Bi intercalation induces a band gap ($E_g=0.42\,$eV) at the Dirac point of graphene and an overall n-doping ($\sim 0.39\,$eV), as seen in angular-resolved photoemission spectroscopy. We attribute the emergence of the band gap to the dislocation network which forms favorably along certain parts of the moir\'e structure induced by the graphene/Ir(111) interface.

Chiral nanoscale pores created during the surface explosion of tartaric acid on Cu(111).

The autocatalytic decomposition of tartaric acid on Cu(111) exhibits unique kinetics, which are linked to a hexagonal surface structure adopted at high coverage. The chirality imposed on the surface by tartaric acid throughout the explosion process is presented, and the hexagonal structure shows promise as a chiral template for enantiospecific surface chemistry.

KAJIAN PEMBUATAN ARANG AKTIF BERBAHAN BAKU BAGAS TEBU MELALUI KOMBINASI PROSES KARBONISASI HIDROTERMAL DAN AKTIVASI KIMIA

ABSTRACT Sugarcane bagasse-based activated carbon which has high adsorption capacity of color in icroporous and mesoporous size in solution phase was produced through combination of hydrothermal carbonization (HTC) and chemical activation processes using phosphoric acid as an activating agent. The activated carbon which was obtained from HTC process at 250° C for 9 hours, followed by chemical activation process at 750° C for 90 minutes with an impregnation ratio of 10% (weight ratio of phosphoric acid to hydrochar) has a BET surface area of 903.47 m2/g, a total pore volume of 0.597 cm3/g (volume composition: 63.32% of micropores and 36.68 % of meso-macropores), an iodine number of 951.99 mg/g, and a methylene blue number of 170.40 mg/g. The FTIR analysis indicated the presence of an aromatic group and a polarity character in the activated carbon produced. The XRD analysis revealed that the activated carbon had hexagonal crystallite and mesoporous surface structures. The SEM analysis showed that the surface topography of the activated carbon had an average pore diameter between 3-10 μm. Keywords: activated carbon, sugarcane bagasse, hydrothermal carbonization, chemical activation

A comparative study of the He–Sb(111) interaction potential from close-coupling calculations and helium atom scattering experiments

The exact elastic close-coupling formalism is used to compare the performance of several interaction potentials suggested in literature for describing the measured elastic diffraction peak intensities in helium scattering experiments. The coupling parameters have been analytically calculated for the corrugated Morse potential on a hexagonal surface structure and adapted for usage with similar interaction potentials. The potentials used have been fitted to previously known bound state energies complemented by two additional levels which are found by improving energy resolution. It is established that the shifted Morse potential reproduces the experimental He–Sb(111) bound state more closely than the other considered potential shapes. The performance of several interaction potentials in describing the elastic scattering intensities is presented and discussed. Morse and Morse-related potentials provide the best compromise for the description of elastic scattering intensities. The different effects of the potential shape were determined by comparing the calculated scattering intensities.

Selective etching of armchair edges in graphite

We present an easy and fast procedure for producing graphene and few layer graphite nanostructures with edges of predefined crystallographic orientation. By annealing graphite in an oxygen containing atmosphere, of controlled composition hexagonal surface structures can be etched in a controlled way. We show that the process can be made crystallographically selective and the resulting edges are of armchair type. The dimensions of the resulting nanostructures can be well controlled by the oxidation rate, through accurately adjusting the etching parameters, such as oxygen concentration, annealing temperature and duration. The oxidation preferentially starts at defect sites either naturally present in the sample or produced on purpose, the latter holding the promise of a more accurate control over the resulting structures.

Strain Effects on the Crystal Growth and Superconducting Properties of Epitaxial Niobium Ultrathin Films

Superconducting ultrathin films grown epitaxially onto crystalline substrates exhibit strained epitaxial growth due to lattice mismatch, which can have a significant effect on their superconducting properties. We present a complete correlation of the surface morphology, crystal growth, strain, microstructure, and superconducting properties in single-crystal Nb(110) thin films sputter deposited on a-plane sapphire substrates. Notably, we observe that the lattice mismatch between Nb and sapphire induces the formation of a hexagonal surface structure during the first three atomic layers. This is followed by a strained bcc Nb(110) phase whose in-plane lattice parameter progressively relaxes to bulk value. Similar lattice relaxation was also observed in the direction perpendicular to the interface using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Significant perpendicular strain in films up to 30 nm thick was found to ultimately affect the superconducting properties of the Nb thin films...

On the relative stabilities of gold nanoparticles

We calculate and compare the relative free energies of ideal/pristine gold nanoparticles for morphologies produced previously in vapor synthesis computer simulations. The results in conjunction with previous work provide a unique and direct quantitative comparison between ideal thermodynamics and kinetics in the synthesis of gold nanoparticles for an identical system. The ideal/pristine free energies suggest that the I(h) morphology was the most stable structure up to the 147(I(h)) followed by the TO(h) for all the remaining nanoparticle sizes. A grouping of m-D(h) structures was identified in the size range N=146-318 with stabilities which were very close to the most stable I(h) and TO(h) structures. The free energy analysis was somewhat at odds with population statistics obtained from our kinetic growth simulations where the I(h) dominated and where very little presumably stable TO(h) nanoparticles were produced, implying that kinetic mechanisms are more influential than thermodynamic considerations. On the other hand other possible reasons for such discrepancies are discussed; one of these includes an interesting observation where the I(h) morphology was found to have a unique ability to incorporate exposed surface disorder such as adatoms into stable hexagonal surface structures through internal and surface structural rearrangements, leading to a possible enhancement in stabilities of I(h)-type morphologies.

Preparation and characterisation of hydroxide stabilised ZnO(0001)–Zn–OH surfaces

Two different approaches under ambient conditions were developed for the preparation of clean, non-reconstructed, single crystalline ZnO(0001)-Zn surfaces. The surface preparation by a wet chemical etching procedure was compared with the same treatment in combination with a subsequent heat treatment in humidified oxygen atmosphere. Depending on the preparation technique, atomically flat terraces with a width of 100 nm to several micrometers were observed using an atomic force microscope (AFM). The obtained surface structures were further characterized by means of angle resolved X-ray photoelectron spectroscopy (AR-XPS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) measurements. Based on these results it is shown that the obtained surfaces are, in contrast to surfaces prepared under UHV conditions, stabilised by the adsorption of a monolayer of hydroxides. The important role of H(2)O during the heat treatment is pointed out by comparing the results of the same heat treatment in the absence of water. H(2)O turned out to play an important role in the reorganization process of the surface at elevated temperatures, thereby yielding extremely large atomically flat terraces. The terminating edges of these terraces were found to include 120 degrees and 60 degrees angles, thus perfectly reflecting the hexagonal surface structure.

Local tunneling barrier height imaging of a reconstructed Pt(1 0 0) surface

The effect of surface reconstruction on work function of a quasi-hexagonal reconstructed Pt(100) surface has been studied by local tunneling barrier height (LBH) imaging with scanning tunneling microscopy (STM). Relatively low LBH is observed at the areas providing the strongly-corrugated geometric structure, where the bright contrast is observed in the STM image. This reduction in the local work function has been interpreted in terms of the dipoles induced by the Smoluchowski smoothing effect. This suggests the reason why the macroscopic work function of the reconstructed Pt(100) surface is lower than that of the Pt(111) surface, despite the similar hexagonal surface structures.

Epitaxial growth of europium on (1 1 0)Nb and (0 0 0 1)Y

A detailed structural analysis of the epitaxial growth of europium using in situ reflection high-energy electron diffraction has been performed for two kinds of buffer layers with different symmetry: (1 1 0)niobium (Nb) and (0 0 0 1)yttrium (Y). Moreover, by varying the preparation conditions of the (1 1 0)Nb layer we get either a reconstructed or an unreconstructed Nb surface, which turns out to have a strong influence on the Eu growth: the reconstructed (1 1 0)Nb surface favours the stabilisation of an Eu hexagonal surface structure, as well as the (0 0 0 1)Y buffer, whereas a pure unreconstructed (1 1 0)Nb surface enables the growth of single crystalline bcc (1 1 0)Eu films. With increasing Eu thickness, the relaxation of the metastable Eu hexagonal surface obtained on (0 0 0 1)Y or on reconstructed (1 1 0)Nb gives rise to a multidomain structure that drastically depends on the nature of the underlying buffer layer.

Hexagonal surface structure during the first stages of niobium growth on sapphire (1120)

A detailed reflection high-energy electron diffraction study of the first stages of the niobium growth on (1120)s sapphire is presented for several substrate temperatures. It is shown that the niobium film exhibits an hexagonal surface structure when the deposited thickness is smaller than a critical value, which, depending on the substrate temperature, varies between 5 and 15 A. For thicknesses larger than this critical thickness, the surface hexagonal structure relaxes to the (110) bcc niobium structure. The hexagonal surface structure is observed for high substrate temperatures (820-410oC) but does not appear when the substrate temperature is 270oC. The epitaxial relationships between the substrate, the surface hexagonal structure of niobium and the cubic niobium phase are presented.

Structural and electronic properties of the Bi/GaP(110) interface.

A systematic investigation of Bi on n-type GaP(110) with scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and ballistic-electron-emission microscopy (BEEM) is presented. The first 3 \AA{} of Bi grows in a quasiordered monolayer, forming alternating chain and vacancy segments along the Ga-P zigzag chains with a periodicity of about 23 \AA{}, which is consistent with the observed 6\ifmmode\times\else\texttimes\fi{}1 low-energy electron diffraction (LEED) pattern. Additional Bi atoms aggregate to form \ensuremath{\simeq}10-\AA{}-high clusters, which suggests a Stranski-Krastanov growth mode. The STS results show that the Bi monolayer is semiconductorlike with a band gap of about 0.55 eV; in contrast, the clusters exhibit metallic character. A 50-\AA{} Bi film exhibited monocrystalline and atomically flat regions \ensuremath{\simeq}1000 \AA{} in extent, which are delineated from similar adjacent regions by height differences equal to a biatomic step. LEED shows an ordered, two-domain hexagonal surface structure that consists of a close-packed-hexagonal arrangement of Bi atoms, as observed by STM. BEEM reveals a uniform Schottky-barrier height of 1.11\ifmmode\pm\else\textpm\fi{}0.02 eV at all measured positions across the sample surface.

Electron spectroscopic studies of tin surface segregation on iron single crystal surfaces

AES, ELS, LEED and XPS investigations of the surface segregation of tin dissolved in a Fe-4wt%Sn alloy were performed in ultra-high vacuum at elevated temperatures. The three low indexed surface orientations (100), (110) and (111) were studied. In all cases, no dependence of the maximum tin surface coverage on temperature was detected within the temperature range from 450 to 650°C. An order-disorder transition was observed by LEED, AES and XPS for the (100) oriented surface during tin segregation. The binding state for the segregated tin atoms abruptly changes at the order-disorder transition as determined by XPS. Similar results were obtained for the (111) surface. A deviating behaviour was observed for the (110) surface orientation, where two different ordered hexagonal surface structures were detected by LEED during tin surface enrichment. The first structure is similar to the diamond structure of pure tin, and the second one corresponds to the formation of a thin layer of the intermetallic compound FeSn on the (110) surface. The electron binding energies of the segregated tin atoms determined by XPS increase with increasing tin coverage on the (110) oriented surface. ELS studies on (100) and (111) oriented surfaces saturated with segregated tin show in comparison with literature data of pure tin a surface plasmon loss peak but no signal for the corresponding bulk loss. An energy loss signal found only for the (110) surface at Sn saturation coverage seems to be characteristic of an intermetallic FeSn surface phase.