Transition from ripples to faceted structures under low-energy argon ion bombardment of silicon: understanding the role of shadowing and sputtering

Abstract

In this study, we have investigated temporal evolution of silicon surface topography under 500-eV argon ion bombardment for two angles of incidence, namely 70° and 72.5°. For both angles, parallel-mode ripples are observed at low fluences (up to 2 × 10¹⁷ ions cm^-2) which undergo a transition to faceted structures at a higher fluence of 5 × 10¹⁷ ions cm^-2. Facet coarsening takes place at further higher fluences. This transition from ripples to faceted structures is attributed to the shadowing effect due to a height difference between peaks and valleys of the ripples. The observed facet coarsening is attributed to a mechanism based on reflection of primary ions from the facets. In addition, the role of sputtering is investigated (for both the angles) by computing the fractional change in sputtering yield and the evolution of surface roughness.

PACS

81.05.Cy, 81.16.Rf, 61.80.Jh, 87.64.Dz     

A multi-attribute decision making approach of mix design based on experimental soil characterization

The clay mineral composition is one of the major factors that governs the physical properties of silty sand subgrade. Therefore, a thorough knowledge of mineral composition is essential to predict the optimum engineering properties of the soil, which is generally characterized by different indices like maximum dry density (MDD), California bearing ratio (CBR), unconfined compressive strength (UCS) and free swelling index (FSI). In this article, a novel multiattribute decision making (MADM) based approach of mix design has been proposed for silty sand–artificial clay mix to improve the characteristic strength of a soil subgrade. Experimental investigation has been carried out in this study to illustrate the proposed approach of selecting appropriate proportion for the soil mix to optimize all the above mentioned engineering properties simultaneously. The results show that a mix proportion containing approximately 90% silty sand plus 10% bentonite soil is the optimal combination in context to the present study. The proposed methodology for optimal decision making to choose appropriate combination of bentonite and silty sand is general in nature and therefore, it can be extended to other problems of selecting mineral compositions.     

Exploring the benefits of vertically staggered wind farms: Understanding the power generation mechanisms of turbines operating at different scales

Wind farms are known to modulate large scale structures in and around the wake regions of the turbines. The potential benefits of placing small hub height, small rotor turbines in between the large turbines in a wind farm to take advantage of such modulated large‐scale eddies are explored using large eddy simulation (LES). The study has been carried out in an infinite wind farm framework invoking an asymptotic limit, and the wind turbines are modeled using an actuator line model. The vertically staggered wind turbine arrangements that are studied in the present work consist of rows of large wind turbines, with rows of smaller wind turbines (ie, smaller rotor size and shorter hub height) placed in between the rows of large turbines. The influence of the hub height of the small turbines, in particular, how it affects the interactions between the large and small turbines and consequently their power, along with the multiscale dynamics involved, has been assessed in the current study. It was found that, in the multiscale layouts, the small turbines at lower hub heights operate more efficiently than their homogeneous single‐scale counterparts. In contrast, the small turbines with higher hub heights incur a loss of power compared with the corresponding single‐scale arrangements.     

Catecholate complexes of zirconium: synthesis,spectroscopic characterization and polymerization studies

Varieties of new catecholate complexes containing zirconium were synthesized in high yields and purity. These derivatives are potent initiators for the ring‐opening polymerization (ROP) of rac‐lactide, l ‐lactide, ?‐caprolactone, δ‐valerolactone, rac‐β‐butyrolactone, ethylene and propylene. The number‐average molecular weights of the resulting polymers are slightly higher than the theoretical molecular weight and they have controlled molecular weight distributions. The isopropoxide moiety in these complexes is responsible for initiating the ROP. For ethylene and propylene polymerization, we were able to achieve good activity using methylaluminoxane as a co‐catalyst. © 2013 Society of Chemical Industry     

Graphene-based flexible and wearable electronics

Graphene with an exceptional combination of electronic,optical and outstanding mechanical features has been proved to lead a completely different kind of 2-D electronics.The most exciting feature of graphene is its ultra-thin thickness,that can be conformally contacted to any kind of rough surface without losing much of its transparency and conductivity.Graphene has been explored demonstrating various prototype flexible electronic applications,however,its potentiality has been proven wherever transparent conductive electrodes (TCEs) are needed in a flexible,stretchable format.Graphene-based TCEs in flexible electronic applications showed greatly superior performance over their conventionally available competitor indium tin oxide (ITO).Moreover,enormous applications have been emerging,especially in wearable devices that can be potentially used in our daily life as well as in biomedical areas.However,the production of high-quality,defect-free large area graphene is still a challenge and the main hurdle in the commercialization of flexible and wearable products.The objective of the present review paper is to summarize the progress made so far in graphene-based flexible and wearable applications.The current developments including challenges and future perspectives are also highlighted.     

An analysis of microstructure and impression creep response of squeeze-cast AZ91–xBi–ySr alloys

ABSTRACT

The present investigation deals with the microstructural modification following the Bi?+?Sr additions to the squeeze-cast AZ91 alloy and its effect on impression creep response. The Bi?+?Sr additions form the Al₄Sr and Sr₂Bi phases besides the α-Mg and β-Mg₁₇Al₁₂ phases, and improves creep resistance of the AZ91 alloy. The AZ91?+?1.0Bi?+?0.5Sr alloy reveals the best creep resistance among the alloys. The stress exponent and the activation energy values of all the alloys are in the range of 4–7 and 100.2–112.7?kJ?mol^?1, respectively, depicting the pipe diffusion-controlled dislocation creep is the governing creep mechanism. The post-creep microstructural study confirms several dislocations pile-ups around the Al₄Sr and Sr₂Bi phases resulting in improved creep resistance of the modified AZ91 alloys.     

An improved statistical approach for moving object detection in thermal video frames

In a video surveillance system, background modeling is assumed to be a fundamental technique for moving object detection. The surveillance system based on thermal video overcomes many challenges, such as background variations, varying light intensity, external illumination source, and so on. This paper presents a new method for background modeling and background subtraction. The method utilizes the combined approach of Fisher's Linear Discriminant and Relative Entropy for pixel based classification and detection of moving objects in thermal video frames. The experimental results show the higher average value of various performance indicators like Accuracy, ROC, and F-measure. In contrast, the percentage of false classification and total error is minimum and also has lesser execution time. The method outperforms when compared with the other existing methods.

     

Brazilian Society of Simulation

Estimation of the parameters of a reducible (inflated common denominator) model for the transfer function matrix of MIMO systems is well known. However, the reduction of the model to the minimal form by pole-zero cancellation is possible only in the noise-free case. This paper presents an algorithm for the estimation of the minimal continuous-time transfer function matrix model. Monte Carlo simulation results are presented for discrete-time and continuous-time models. Least-squares and generalized least-squares methods have been used in both cases. An asymptotic analysis of convergence has also been provided for these models in the noise-free case. The computation times and space complexities of different variants of the algorithm are compared. The results show that in noisy situations, obtaining a discrete-time model by discretizing an estimated continuous-time model may be a viable proposition     

Highly Flexible Hybrid CMOS Inverter Based on Si Nanomembrane and Molybdenum Disulfide

2D semiconductor materials are being considered for next generation electronic device application such as thin‐film transistors and complementary metal–oxide–semiconductor (CMOS) circuit due to their unique structural and superior electronics properties. Various approaches have already been taken to fabricate 2D complementary logics circuits. However, those CMOS devices mostly demonstrated based on exfoliated 2D materials show the performance of a single device. In this work, the design and fabrication of a complementary inverter is experimentally reported, based on a chemical vapor deposition MoS₂ n‐type transistor and a Si nanomembrane p‐type transistor on the same substrate. The advantages offered by such CMOS configuration allow to fabricate large area wafer scale integration of high performance Si technology with transition‐metal dichalcogenide materials. The fabricated hetero‐CMOS inverters which are composed of two isolated transistors exhibit a novel high performance air‐stable voltage transfer characteristic with different supply voltages, with a maximum voltage gain of ≈16, and sub‐nano watt power consumption. Moreover, the logic gates have been integrated on a plastic substrate and displayed reliable electrical properties paving a realistic path for the fabrication of flexible/transparent CMOS circuits in 2D electronics.     

Genetic programming-assisted multi-scale optimization for multi-objective dynamic performance of laminated composites: the advantage of more elementary-level analyses

Neural Computing and Applications - High-fidelity multi-scale design optimization of many real-life applications in structural engineering still remains largely intractable due to the...