Average Aspect Ratio Research Articles

Effects of different carboxyl additives on the growth habits of hemihydrate gypsum crystals

Hemihydrate gypsum whiskers with high aspect ratios were prepared by using phosphogypsum as the raw material through the autoclaved method. The effects of additives containing different carboxyl groups, namely, sodium stearate, sodium citrate and EDTA-tetrasodium, on the average length and average aspect ratio of the hemihydrate gypsum whiskers were studied. The results show that hemihydrate gypsum whiskers with longer average length and larger average length–diameter ratio can be prepared by adding sodium stearate or EDTA-tetrasodium. The crystallisation behaviour of hemihydrate gypsum crystals with different crystal faces under different carboxyl additives was investigated through XRD, FTIR, XPS, and molecular dynamics simulation. XRD, FTIR, XPS results demonstrated that different carboxyl additives had less effect on promoting hemihydrate gypsum crystal growth along the C-axis direction at increasing number of carboxyl groups, and sodium citrate reacted with calcium ions, while sodium stearate and EDTA-tetrasodium did not react with calcium ions. Molecular dynamics simulation results manifested that the order of interaction energy between disparate carboxyl additives and hemihydrate gypsum crystal along the C-axis crystal plane was ΔE (EDTA-tetrasodium) < ΔE (sodium citrate) < ΔE (sodium stearate), indicating that the adsorption of various carboxyl additives on hemihydrate gypsum crystal along the C-axis crystal plane was related to the number of carboxyl groups.

Fabrication of hierarchical hybrid ZnO/Au micro-/nanostructures for efficient dye degradation: role of gold nanostructures in photophysical process

In this work, colloidal solutions of gold nanoparticles (AuNPs) with an average diameter of 16 nm and gold nanorods (AuNRs) with an average aspect ratio of 6.8 were synthesized. These gold nanostructures were decorated on nanosheets assembled 3D ZnO microflower (ZnO-MF) synthesized via facile and cost-effective co-precipitation method. Plasmonic gold nanostructures act as optical concentrators and a reservoir of electrons under LSPR excitation. They extend the light harvesting capability of ZnO from UV–VIS–NIR region, promotes interfacial charge transfer process and helps in electron-hole pair separation. We report the occurrence of FRET (Fluorescence Resonance Energy Transfer) between defect rich ZnO-MF and gold nanostructures under UV light excitation as evident from micro-PL spectra. This triggers surface plasmon resonance in gold nanostructures which causes direct transfer of hot electrons to ZnO-MF. Time-resolved Photoluminescence of the hybrid samples monitored at near band edge of ZnO shows elongated decay kinetics as compared to bare samples which could be attributed to direct transfer of hot electrons from gold to conduction band of ZnO-MF after LSPR excitation. Thereafter, the photocatalytic activity of the hybrids is evaluated by degradation of four different dyes under sunlight. ZnO-MF/AuNPs exhibited superior photocatalytic activity compared to ZnO-MF/AuNRs. This could be attributed to numerous reasons like better energy transfer efficiency, effective near-field enhancement, small size of AuNPs and enhanced electron-hole pair separation which makes ZnO-MF/AuNPs a promising photocatalyst.

Distal femoral arthropometry in Nigerians and its correlation to total knee replacement implants.

Total Knee replacement (TKR) is performed to relieve pain and restore both the mechanical axis and joint line whenever indicated. Most of prostheses being used for TKR were manufactured using dimensions from Caucasians' measurements. This study documented the dimensions of distal femora of Nigerians and correlated the dimensions with different TKR prostheses. Fifty-six matured femora were measured. Dimensions of distal femora from other regions were retrieved from published articles. The dimensions of TKR prosthesis were extracted from product monographs. Analyses were done with Microsoft excel 2010 (Microsoft Corporation, Redmond, Washington, United States) and STATA version 13 (StataCorp, Texas. USA). Statistical significance was set at p ≤ 0.05. The average Mediolateral dimension was 79.3 ± 4.4 mm. The anterioposterior dimensions of the medial and lateral condyles were 63.7 ± 3.6 mm and 64.9 ± 3.3 mm respectively. There were no significant differences between the left and right distal femur. The average aspect ratio calculated was1.23 ± 0.05. There was a mismatch of aspect ratio of the distal femora and those of the prostheses. Equations that can be useful both clinically and in forensic medicine were generated. This study has provided measurements that can be considered when the designing of a suitable femoral component of total knee prosthesis for Nigerians. This study also provided equations that can be used to estimate the dimensions of the medial and the lateral condyles and femoral length from parts of distal femur in forensic medicine. Self-funded.

Work hardening and softening behavior of Mg–Zn–Ca alloy influenced by deformable Ti particles

Pure titanium particles reinforced Mg–6Zn-0.2Ca magnesium matrix composites were fabricated by semi-solid stirring casting followed by hot extrusion in this work. The microstructures and mechanical properties of the Mg–6Zn-0.2Ca alloy and its composites were studied. The Ti particles in as-extruded composites are significantly elongated along the extrusion direction. The average aspect ratio of Ti particles increases while the average size decreases, with the extrusion temperature decreasing. Ti particles promote the dynamic recrystallization of the matrix alloy, break the long-strip Ca2Mg6Zn3 phases and refine the size of MgZn2 phases in the Mg–6Zn-0.2Ca matrix, especially for low extrusion temperatures. The Tip/Mg–6Zn-0.2Ca composite extruded at 240 °C exhibited a high yield strength (YS) of 383.6 MPa with an ultimate tensile strength (UTS) of 404.8 MPa and a decent elongation to failure (EL) of 4.8%. The high strength is associated with fine grains, nano-precipitates as well as Ti particles. In addition, the work hardening rate of Tip/Mg–6Zn-0.2Ca composite is higher than that of Mg–6Zn-0.2Ca alloy at the early stage of plastic deformation due to the combined effects of the elongated Ti particles, the grain refinement and nano-scale MgZn2 precipitates. However, the work hardening rate of the composite decreases faster owing to dislocations cross-slip. And the composite is easier to soften, which results from grain boundary sliding of fine grains and work hardening of deformable Ti particles.

A scattering function for correlated lamellae

Melt crystallized polymers display an emergent, multi-hierarchical, ordered structure made up of stacked lamellar single crystals that form fibrous or other meso structures which, in turn, form macroscopic crystallites. A dominant feature of small-angle scattering from these complex assemblies is a correlation peak associated with the stacking period. A new model-based function is proposed for small-angle scattering data from such correlated lamellar multi-hierarchical structures. Generally, routine use of scattering data has been limited to a 1-d analysis to determine the long period from Lorentz corrected data (I(q)q2 versus q). Fourier transforms of the data are sometimes used to determine the 1-d pairwise correlation function for the electron-density distribution which has been further analyzed in terms of the structure of these materials. A simple 1-d fitting model limited to infinite width 2-d sheets was introduced by Hermans (1944; Hosemann, 1950) [1,2] in the 1940s with some success. A new approach, the Unified Born-Green Function (UBG), is proposed that uses the Unified Function as adapted to correlated lamellar structures and incorporates a Born-Green description of one-dimensional correlations. The UBG fit allows quantification of the average lamellar aspect ratio, the local degree of crystallinity within a stack, quantification of the stacking versus non-stacking amorphous, and two types of disorder in addition to the stacking period and lamellar thickness. UBG can account for higher levels of structure such as crystalline domains in block copolymers and convoluted lamellar structure. The UBG fit is compared to the Hermans (1944; Hosemann, 1950) [1,2] and a hybrid-Hermans function. Fits to data sets from a wide range of polyethylene are shown ranging from molecular weight standard samples that are isothermally crystallized, to commercial HDPE quenched from the melt and a metallocene blown film sample. Several other examples from the literature are explored. It is shown that the Unified fit allows for new understanding of the impact of thermal and mechanical history, chain structure, fillers, nucleating agents, and additives on the crystalline structure and the resulting physical properties. Limitations of the UBG approach are noted.

Optimization Strategy of Traditional Block Form Based on Field Investigation-A Case Study of Xi'an Baxian'an, China.

Rapid urbanization has caused environmental problems such as the urban heat island and air pollution, which are unfavorable to residents. Urban traditional blocks are facing the dual challenges of restoration and protection. This paper proposes adaptive transformation strategies for improving the microclimate of traditional areas. We selected Baxian’an Block in Xi’an city, simulated the air temperature and wind speed during summer and winter using ENVI-met, and studied the correlationship between morphological parameters (average building height, building density, enclosure degree, height fall, aspect ratio, and sky view factor) and air temperature and wind speed ratio. The case study revealed that the wind speed ratio of Baxian’an is relatively different in summer, reaching a maximum of 0.61, meaning that the ventilation capacity is significantly affected by the architectural form of the block. Finally, suggestions for the optimal design of the block’s form are provided: the building density should be less than 50%, the average building height should be more than 50 m, the enclosure degree should be less than 0.2, the height fall should be more than 41.7 m, and the sky view factor should be less than 0.5. This study can provide data and support for improving the planning and design standards of traditional residential areas.

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Preparation of hemihydrate gypsum with controllable morphology in Glycerol-NaCl-Water solutions with maleic acid

The synthesis of hemihydrate gypsum (α-HH) crystals with a low aspect ratio is of great significance to practical production for the effective utilization of flue gas desulfurization (FGD) gypsum. In this work, the hexagonal prismatic α-HH crystals with controllable morphology were prepared in Glycerol-NaCl-Water solutions with maleic acid, and the average aspect ratio of α-HH crystals decreased from 19.49 to 1.10. The phase transformation time decreased with the NaCl concentration, increased with the pH of the reaction solutions, but higher pH destroyed the crystal structure of α-HH. The phase conversion process involves the dissolution of FGD gypsum and nucleation of α-HH crystals was immediately observed by a microscope in real time. Maleic acid might adsorb on the (204), (200), and (020) crystal planes of α-HH and retarded or promoted the crystal growth along different directions, thus realizing the effective control of α-HH crystal morphology.

Comparison of cellulose nanocrystals from pineapple residues and its preliminary application for Pickering emulsions

Pineapple, as a world-famous tropical fruit, is also prone to produce by-products rich in cellulose. In this study, different sections of pineapple, including pineapple core (PC), pineapple pulp (PPu), pineapple leaf (PL) and pineapple peel (PPe) were used for production of pineapple cellulose nanocrystals (PCNCs) by sulfuric acid hydrolysis. The crystallinity of PCNCs from PC, PPu, PL and PPe were 57.81%, 55.68%, 59.19% and 53.58%, respectively, and the thermal stability of PCNCs in order was PC > PL > PPe > PPu. The prepared PCNCs from PC, PPu, PL and PPe were needle like structure at the average aspect ratios of 14.2, 5.6, 5.5, and 14.8, respectively. Additionally, the differences in the structure and properties of PCNCs affected the stability of the prepared Pickering emulsions, which ranked as PPu > PPe > PL > PC. The Pickering emulsions stabilized by PCNCs prepared from PPu could be stored stably for more than 50 d. These results show the differences of PCNCs from four sections of pineapple, and provide isolated raw material selection for the further application of PCNCs.

Novel approaches on bulk‐loading of large scale spatial datasets

SummaryIndex structures that are bulk‐loaded adaptively based on the query workload have been the subject of many database research, primarily in conventional databases holding one‐dimensional data. Similar problems are also valid for spatial databases, and novel approaches are needed in these systems. In this study, we first consider the adaptive indexing approaches in a broad sense and then specifically investigate some possible forms of adaptivity on bulk‐loading of large spatial datasets while retaining some core mechanics of well‐known spatial data structures. In our first design, we examined how the internal configuration of the R‐tree spatial index could be better for various workload properties, such as the workload's average aspect ratio. Our experiments observed that Adaptive Sort‐Tile‐Recursive (STR)‐tree performs better than the original STR‐tree. Our second design, the main contribution of this paper, focused on incremental indexing, another form of adaptivity. We concentrate on the data‐to‐insight latency and loaded spatial data faster within this multi‐stage process. We used the Partitioned B‐tree loaded with Morton codes of spatial objects to achieve this improvement by compromising spatial proximity. Finally, the response time of the first query in our design has been better than using the ordinary STR‐tree index by a factor of 34%.

Treemap Layout Based on Monte Carlo Tree Search

<p indent=0mm>Treemaps are a commonly used method for hierarchical data visualization. The previous research shows that three treemap layout algorithms(SQR, STR, SPI) that meet the principle of gradually adding points on four common optimization indicators(average aspect ratio, stability, consistent data, readability) have their own advantages and disadvantages. Both Strip and Spiral algorithms result in relatively large aspect ratio of layouts, and the squarified treemap has some room for optimization in the aspect ratio. Based on Monte Carlo tree search, the corresponding search tree is constructed while laying out the treemap and the upper confidence bound formula is used as the selection criterion for the search path. For the three layout algorithms, the arithmetic average aspect ratio and the newly proposed weighted aspect ratio are improved within acceptable time for users. To show the effectiveness of the algorithm, the evaluation with the constructed single-layer dataset which with 3 different distributions and 7 different scales and multi-layer real dataset is conducted and then the results are compared with the original algorithm. The guidelines for users to select a suitable layout algorithm and set proper parameters are also provided.

Foam Flow in Different Pore Systems—Part 2: The Roles of Pore Attributes on the Limiting Capillary Pressure, Trapping Coefficient, and Relative Permeability of Foamed Gas

Summary The limiting capillary pressure of foam (Pc*) and foam trapping in porous media are pore-scale foam properties that affect foam transport in porous media. They are strongly influenced by the characteristics of rock pores and throats. Because of experimental limitations, these foam properties are difficult to measure at core scale. As a result, our understanding of their relationship with different pore characteristics is limited. In this paper, novel coreflood and graphical analysis techniques were used to measure Pc* and the foam-trapping coefficient (FTC) at core scale. FTC is a new parameter synonymous to Land’s (1968) trapping coefficient, which describes foam-trapping behavior across an entire range of saturation as opposed to a single endpoint trapped saturation. The scalability of these two foam properties with permeability and other pore characteristics [average pore size (PS), average throat size (TS), average aspect ratio (AR), coordination number (CN), surface area/volume ratio, and reservoir-quality index (RQI)] were also investigated. Pore characteristics of 12 different rock samples were measured from 3D pore-network models generated from high-resolution X-ray computed-microtomography images. The heterogeneity of the rock samples were quantified by the Dykstra-Parsons index (Dysktra and Parsons 1950), while the RQI and J-function methods were used to classify them according to their storage and flow properties. Each of the measured pore characteristics and their combination [combined pore character (CPC)] were then correlated with Pc* and FTC to understand their respective roles. Furthermore, the data points obtained from the graphical analysis of the coreflood data provided the required input data for a mechanistic foam model for relative permeability of foamed gas (Kovscek and Radke 1994). The estimated relative permeability of foamed gas was then used to study foam mobility in the different pore geometries. The overall results showed the following: P c * has strong negative correlations with all pore characteristics except AR, which has a weak positive correlation. P c * has the strongest correlation with RQI, CPC, and permeability; a moderate correlation with CN and TS; and a very weak correlation with PS. Foam trapping has positive correlations with all pore characteristics except AR, which has a negative correlation. Low AR appears to be responsible for significant trapping of foam in high-permeability rocks. Low AR favors more foam trapping, while high AR favors trapping of oil and gas during water imbibition in water-wet rocks. Foam trapping appears to have the dominant control on foam mobility.

Foam Flow in Different Pore Systems—Part 1: The Roles of Pore Attributes and Their Variation on Trapping and Apparent Viscosity of Foam

Summary Lateral propagation of foam in heterogeneous reservoirs, where pore geometries vary laterally, depends on the roles of pore geometries on the foam properties. In this paper, the pore attributes of 12 different rock samples were characterized in terms of porosity, permeability, pore shape, pore size, throat size, aspect ratio, coordination number, and log mean of surface relaxation times (T2LM). These were measured from gas porosimeter and permeameter, X-ray microcomputed tomography (CT)-based pore-network models, thin-section photomicrographs, and nuclear magnetic resonance (NMR) surface relaxometry. The samples have a wide range of porosity: 12 to 29%; permeability: 1 to 5,000 md; average pore size: 3.7 to 9 µm; average throat size: 2.4 to 8 µm; average aspect ratio: 1 to 1.7; average coordination number: 2.6 to 5.2; and T2LM: 9.4 to 740 ms. Nitrogen foam flow experiments (without oil) were then conducted on each rock sample using a specialized coreflood apparatus. A graphical analysis of the coreflood data was used to estimate the total saturation of trapped foam (10 to 66%), flowing foam (3 to 14%), and apparent viscosity of foam (3.2 to 73 cp). Trapped foam saturation and apparent viscosity values were then correlated with each of the measured pore attributes. The results revealed that all pore attributes, except aspect ratio, have positive correlations with foam trapping and apparent viscosity. The best correlation with trapped foam saturation was obtained when the most influential pore attributes (pore size, throat size, aspect ratio, and coordination number) were combined into a single mathematical function. Foam apparent viscosity also appears to be mostly influenced by trapped foam saturation, permeability, and coordination number of pore systems. Trapping is also likely enhanced by the presence of fenestral or channel pores. Furthermore, the shape and angularity of pores seem to facilitate snap-off and trapping of foam, because rock samples with angular pores trapped the highest foam saturation compared with other samples with rounded and subrounded pores. It was also shown that the correlation between trapped foam saturation (and foam apparent viscosity) and the absolute permeability of porous media may reverse at some high-permeability values (greater than several darcies), when one or both of the following conditions exist: (1) The aspect ratio of a lower-permeability porous medium is lower than that of a higher-permeability porous medium, and (2) the coordination number of a lower-permeability porous medium is higher than that of a higher-permeability porous medium. Finally, T2LM showed a good correlation with foam trapping, making NMR logging a prospective tool for pre-evaluating foam performance in targeted reservoir sections.

Pour point depression and flow improvement of waxy crude oil using polyethylene glycol esters of cashew nut shell liquid

Wax crystallization and deposition is a major flow assurance problem in production and transportation of waxy crude oil. Conventional flow improvers are mainly high molecular weight synthetic polymers, many of which are eco-toxic. Bio-based flow improvers derived from natural products are promising as inexpensive, eco-friendly alternatives to existing products. In this study, natural cashew nut shell liquid (CNSL) extracted from waste shells of Anacardium occidentale was esterified with polyethylene glycol (PEG). CNSL derivative reduced the pour point of waxy crude oil by 12 °C at 1000 ppm. The effects of CNSL derivatives on wax crystal morphology and micro-structure were studied by cross-polarized microscopy. Micrographs were processed and analyzed with ImageJ software. Addition of CNSL derivatives to oil resulted in changes in wax crystal morphology and micro-structure evidenced by a reduction in average crystal Feret diameter and aspect ratio and increase in boundary fractal dimension, indicative of formation of increasing number of smaller, rounder crystals. Effect of the additives on flow properties of the waxy oil was determined using a co-axial cylinder rotational viscometer. Dynamic viscosity of oil at shear rate of 17 s−1 was reduced by 79.7–90.5%. CNSL-PEG esters show good prospects as low-cost additives for production, storage and pipeline transportation of waxy crude oil.

Crack geometry of serpentinized peridotites inferred from onboard ultrasonic data from the Oman Drilling Project

To assess the geometry of cracks in highly altered peridotites, we analyzed the ultrasonic velocity of serpentinized dunites and harzburgites collected by the Oman Drilling Project (Holes BA1B, 3A, and 4A). First, we estimated the hydrated fraction from grain density to obtain the porosity-free matrix velocity, which indicated complete serpentinization at shallow depths and decreasing hydration at greater depths. We assume that the difference between the solid matrix and measured onboard ultrasonic velocity is attributed to cracks with a spheroidal shape in the samples. Application of the effective medium theory to onboard data, such as P-wave velocity and porosity, indicates that the average pore aspect ratio is mostly between 0.1 and 0.01, and crack density varies from 0.58 to 0.02. We found a positive relationship between aspect ratio and hydrated fraction, suggesting a change in crack shape related to dissolution–precipitation processes during hydration. The relatively high aspect ratio and hence high fluid flux at shallow depths are also consistent with the onboard resistivity data and present-day hydration processes inferred from the borehole fluid chemistry. The inversion of ultrasonic data provides a series of elastic moduli that can be used to make a rough approximation of Poisson's ratio from the onboard data, which is a key physical property for interpreting geophysical observations in the oceanic lithosphere.

Microconical Structure Formation and Field Emission From Atomically Heterogeneous Surfaces Created by Microwave Plasma–Based Low-Energy Ion Beams

We report the formation of self-organized microconical arrays on copper surface when exposed to high flux (5.4 × 1015 cm−2 s−1) of 2 keV argon ion beams at normal incidence. The created microconical arrays are explored for field emission properties. The surface morphologies are investigated by scanning electron microscopy and atomic force microscopy. The local work function variation is analyzed by Kelvin probe force microscopy, and the argon content in the irradiated layer is measured with X-ray Photoelectron Spectroscopy. The average aspect ratio (base width/height) of microstructures for individual irradiated samples is found to increase from 0.7 to 1.5 with a decrease in ion fluence. The ion concentration is highest (3.89 %) for a fluence of 4.7 × 1018 cm−2, which asserts the formation of atomically heterogeneous surface due to subsurface ion implantation. An enhancement in the field emission properties of the argon ion–treated copper substrates at a fluence of 4.7 × 1018 cm−2 with a low turn-on voltage of 2.33 kV and with electron emission current 0.5 nA has been observed. From the Fowler–Nordheim equations, the field enhancement factor is calculated to be 5,561 for pristine copper, which gets enhanced by a factor of 2–8 times for irradiated substrates. A parametric model is considered, by taking into account the modified local work function caused due to structural undulations of the microstructures and presence of implanted argon ions, for explaining the experimental results on the field enhancement factor and emission current.

Yield stress and wall slip of kaolinite networks

In this work, the nonlinear rheological properties of kaolinite suspensions as a model fluid were studied. Three kaolinites with different average particle, aspect ratio and asperity were used to gain a deeper understanding of the effects of particle's geometry on yielding, rheology, and apparent slip velocity over a wide range of concentrations in the semi-concentrated to concentrated regime. To reveal the impact of geometry on kaolinite suspension's rheology, atomic force microscopy was employed, thus revealing unique information about the particle's structural differences. The apparent slip velocity was studied through the application of the Mooney technique using experimental data from parallel-plate geometry at various gap spacings. Sandpaper of varying grit was used to eliminate slip and estimate the true rheological parameters including the yield stress of these materials. Kaolinite suspensions were found to follow a Herschel–Bulkley model with yield stress that increases with concentration irrespective of the type of kaolinite particles. The aspect ratio and asperity of particles were found to alter their slip behavior by enabling the kaolinite network to have a tunable yield stress. It was also determined that the existence of resilient larger clusters at higher shear rates often induce higher slip effects.

Effects of different types of sintering additives and post-heat treatment (PHT) on the mechanical properties of SHS-fabricated Si3N4 ceramics

Porous silicon nitride (Si3N4) ceramics were fabricated by self-propagating high temperature synthesis (SHS) using Si, Si3N4 and sintering additive as raw materials. Effects of different types of sintering additives with varied ionic radius (La2O3, Sm2O3, Y2O3, and Lu2O3) on the phase compositions, development of Si3N4 grains and flexural strength (especially high-temperature flexural strength) were researched. Si3N4 ceramics doped with sintering additive of higher ionic radius had higher average aspect ratio, improved room-temperature flexural strength but degraded high-temperature flexural strength. Besides, post-heat treatment (PHT) was conducted to crystallize amorphous grain boundary phase thus improving the creep resistance and high-temperature flexural strength of SHS-fabricated Si3N4 ceramics. Excellent high-temperature flexural strength of 140 MPa~159 MPa and improved strength retention were achieved after PHT at 1400 °C.

Three-step seedless synthesis of ultralong gold nanorods

Ultralong gold nanorods with an average aspect ratio up to 77 and average length up to 1.6 μm were obtained by using the three-step seedless wet chemistry growth method. The prepared ultralong gold nanorods were pentatwinned. The effects of the amount transferred from flask B to C, and the pH value in the growth solution C on the synthesized ultralong gold nanorods were investigated by using the scanning electron microscopy images. Results showed that ultralong gold nanorods with tunable average aspect ratio from 24 to 77 were obtained by changing the amount transferred from flask B to C and the pH value in the growth solution C. Due to the large aspect ratio of the prepared gold nanorods, the longitudinal surface plasmon resonance wavelength of the ultralong gold nanorods was expected in the infrared wavelength region. Moreover, 2 μm mid-infrared pulsed laser output was achieved in a passively Q-switched solid-state laser by using the prepared ultralong gold nanorods as the saturable absorber. Our method offers a new facile strategy to obtain ultralong gold nanorods with tunable aspect ratios, which have wide applications in areas such as photonics and optoelectronics.

Interaction of size-selected Ag-clusters on Au-thin films: a composition study with in-situ XPS analysis at an elevated temperature

In this paper, we describe a novel method of synthesis of bimetallic Ag–Au alloy nanoparticles with an estimated Ag to Au concentration ratio of ∼3:1 by using a gas-aggregation cluster source. The real time chemical changes occurred on the surface of the alloy film during different stages of annealing at an elevated temperature are observed by in-situ x-ray photoelectron spectroscopy analysis. It is found that the concentration of both Ag and Au of the alloy film simultaneously decreases with the increase of the annealing time. The chemical states of the elements present on the surface are analyzed from the HR-XPS data, which are recorded for the dominant elements present on the surface. From the analyses, it is found that a small part of metallic Ag gets oxidized for higher annealing time whereas no trace of oxidation of Au is observed. The surface morphology of the as-deposited and post-annealed alloy films are characterised by FESEM and AFM measurements. Due to thermal diffusion of Ag and Au, resultant narrow size distributions of the bimetallic Ag–Au nanoparticles are observed on the surface. The film morphologies suggest that the evolutions of bimetallic Ag–Au nanoparticles are nearly spherical in shape with an average aspect ratio value of ∼1.5.