Sharif Digital Repository

Nowadays precise nano positioning plays an important role in micro systems. Precise positioning at nano scale plays a basic role in nano science such as micro -robotics, solid state physics and photonics. Manipulating matter in a molecular scale creates a dramatic change and restruturing in macro scale engineering. During this research a novel TEM micro actuator is designed and fabricated based on calibration criteria. This structure was fabricated with SOI wafer (silicon on insulator) in micro scale level for the first time in Iran. This compliant consists of 12 TEM actuators end in 3DOF (In-plane) motion. The new micro actuator operates based on the thermal expansion due to voltage. Each... 

Currently, precision positioning plays a pivotal role in technology. The need for accurate positioning in applications such as robotics, optoelectronics and micro and nano technology increases day by day. To begin with, we wanted to make a miniature prototype of a micro actuator but in this regard, we are faced with several problems. Some major problems were the high cost of this prototype plus the fact that we did not have the necessary equipment with acceptable resolution for making such a system, so we decided to decrease the scale and build it in micro scale which is accessible for us. The main idea and design of this micro actuator is by Mrs. Akbari. During this project, the researcher... 

Humans need the five senses to understand and interact constructively with their surrounding environment; in the world of robots and intelligent systems, this is achieved using sensors. In the modern world, tactile sensors based on triboelectric effect play a prominent role in important application areas such as health monitoring, human-computer interaction, robotics, pressure mapping, and electronic signature. Triboelectric nanogenerators (TENGs) are one type of energy harvesting systems that convert mechanical energy into electrical energy. In these sensors, due to the contact and touch with the triboelectric material, an electric charge is generated and induced into the electrode, then... 

Nuclear energy is one of the most important sources of energy from the economical point of view and also in terms of cleanliness and safety. Hence, strategically, uranium is one of the most basic elements of the earth and nowadays, the importance of this element is more marked due to the nuclear industry developement. Therefore, uranium recovery from the wastes generated during nuclear fuel production in Isfahan’s uranium conversion plant- in which yellow cake is converted to uranium hexafluoride- is quite pivotal. In this experimental research, we have to remove Fluoride from waste after dissolution by several methods like precipitation. After that uranium is extracted from the sludge of... 

Metal matrix composites (MMCs) have received considerable attention due to their excellent engineering properties, but their poor machinability has been the main deterrent to their substitution for metal parts. The hardness and abrasive nature of reinforcement phase causes rapid tool wear during machining and, consequently, high machining costs. This paper discusses an experimental investigation on the machinability of Al-SiC particulate metal matrix composite produced by powder metallurgical process with , and %SiC. Continuous dry turning of round composite bars using titanium carbide inserts has been selected as the test method. The influence of machining parameters, e.g. cutting speed,... 

Due to reduced Non-Recurring Engineering (NRE) costs, shorter time to market, design flexibility, and reprogramming capability of Field-Programmable Gate Arrays (FPGAs) as compared to Application-Specific Integrated Circuits (ASICs), FPGAs has been raised as a suitable substrate for implementation of digital systems. However, the high flexibility of reconfigurable devices leads to great power consumption, chip area, and reliability difference between ASICs and FPGAs. In addition, with the advent of multi-tenant FPGAs in cloud computing environments, it has been shown that crosstalk side-channel attack, which can be used by a malicious IP to leak valuable information, has become an urgent... 

Significant increase of static power with downscaling of transistor feature size and threshold voltage has lead to the end of Dennard scaling. This obstacle has put a Power Wall to further integration of CMOS technology in Field Programmable Gate Arrays (FPGAs). An efficient solution to cope with this obstacle is to apply power gating to the inactive fractions of a single die, referred to as Dark Silicon. Previous studies employing power gating on SRAM-based FPGAs have primarily focused on using large-input Look-up Tables (LUTs) which suffer from poor logic utilization, and subsequently, limiting the benefits of power gating techniques. This thesis proposes a heterogeneous Power-Efficient... 

Growing transistor counts, limited power budgets, and the breakdown of voltage scaling are currently conspiring to create a utilization wall that limits the fraction of a chip that can run at full speed at one time. This concept is the basis of the Dark Silicon definition. To address this issue, it is needed a structure to guaranty Limited power budget and obtain sufficient flexibility and performance for different applications with variety communication needs. Regarding to this structure, our aim is to present a platform for Networks-on-Chip that uses clustering and resource sharing among cores. Moreover, as task mapping on processing elements in NOCs is one of the most effective way to... 

Since 2005, processor designers have increased core counts to exploit Moore’s Law scaling, rather than focusing on single-core performance. For decades, this approach provides desired performance for parallel and multithreaded workloads. On the other hand, rising of utilization wall limits the number of transistors that can be powered on in chip and result in a large region to be dark. So, same as before trend for performance scaling in future multi processor, an appropriate architecture is essential. There are some structures for this era which used specialization approach to cope with the limited power budget. Therefore, in this thesis, we propose a general-purpose platform that provides... 

The exact analytical elastic fields within a double-walled silicon nano-tube with a thin layer of SiOx coating associated with surface/ interface effects as well as the classical theory of elasticity due to the presence of an edge dislocation with an arbitrary Burger’s vector and position inside of the silicon is determined via complex potential function method. Stress contours within surface elasticity and classical theory are given, and both theory results are compared. Then, the effects of surface Lamé Constants, magnitude and direction of Burger’s vector, shear modulus, nano-tube size, and position of the edge dislocation on the distribution of stress components are illustrated, and the... 

By employing first principles density functional theory-based (DFT) molecular dynamics (MD), the influences of dangling and floating bonds as well as distorted tetrahedral bonds are studied on the mechanical, physical, and electronic properties of amorphous Si (a-Si). For further examination of the effects of these geometrical defects, two distinct amorphous samples, namely as-quenched and annealed are generated and examined. To verify the validity of the representative cells, the obtained radial distribution function, pair correlation function, and cohesive energy are compared with those corresponding results presented in the literature. Moreover, the surface energy is calculated at final... 

The band gap offset is an effect of coordination numbers (CNs) of atoms reduction at the edge of transversal cross-section Si nanowires (SiNWs) which would be of increasingly important for greater shell-core ratio sections. In this paper, a hierarchical multi-scale modeling has been developed to simulate edge effect on the band gap shift of SiNWs due to geometry effect induced strain in the self-equilibrium state. Classical Molecular Dynamics (MD) approach and Finite Element Method (FEM) are used in the micro (atomic) and macro scale levels, respectively. Using the Cauchy-Born (CB) hypothesis as a correlator of continuum and atomic properties, the atomic positions are related to the... 

The use of superhydrophobic surfaces is one the most promising methods for reducing the friction and increasing the flow rate in fluid transfer systems. Since in such systems the surface structure plays a key role, in the first part of this study, the performance of the hierarchical nanostructures is explored. These nanostructures are inspired by the superhydrophobic surface of the lotus leaf. The flow is considered between two walls with hierarchical nanostructures and simulate the system via the molecular dynamics (MD) method. The size of the nanostructures and the distance between them have been studied to find whether a design with maximum flow rate exists. The nanostructures have two... 

In Li-ion batteries, large volume changes of electrodes with high capacity, such as silicon electrodes during charging and discharging processes (insertion/extraction of lithium into/from the electrode), lead to restrictions on the use of this type of electrode. Given the very high capacity of silicon, predicting and modeling the behavior of silicon electrodes during electrochemical cycles is important and is also addressed in this thesis. First, using the theory of linear elasticity, relations are proposed that couple the diffusion of particles with small elastic deformation. The effect of hydrostatic stress on diffusion and stresses is investigated in lithiation processes. Then, the... 

The new generation of electronic devices including 5G internet, wearable electronics, LED optoelectronics or cloud computing devices have higher power density as their computing power increases and their sizes reduce. The increase in power density leads to higher heat generation and consequently higher operating temperature which reduces their lifetime and reliability. In recent years development of novel solutions for electronic cooling has been persued. Thermal interface material that inserted between heat source and heat sink is the main component in electronic cooling. These materials consists of a polymeric base that filled with highly thermally conductive solid particles. By emergence... 

Among the various materials, silicon anodes have the highest lithium absorption in lithium-ion batteries. But this high lithium absorption capacity can cause 300 percent volume expansion and large stresses. Experimental observations show that charge and discharge cycles may cause plastic deformation in some parts of the electrode particle. On the other hand, there is a possibility of a ratcheting phenomenon due to changing in elastic properties of the electrode material during the charging and discharging processes. However, this phenomenon has not been reported for silicon spherical electrode particles yet.This study aims to model the elastic-plastic behavior of silicon spherical electrode... 

Thin film solar cells have low efficiency compared to crystalline silicon solar cells; however, they are low-cost and flexible. In manufacturing these solar cells, thin films are deposited at high temperatures (higher than 200℃) on a thick metal, plastic, or glass substrate using sputtering and plasma enhanced chemical vapor deposition (PECVD) methods. Since the thin films and substrate have different thermal expansion coefficients, cooling the system from deposition temperature to room temperature induces thermal residual stresses in both the films and substrate. In addition, these stresses, especially those induced in the amorphous silicon layer can change the carrier mobility and band gap... 

Electrochemical deposition of multilayer coatings is one of the surface engineering techniques to create thin surface layers with a controlled structure in order to create desirable surface properties. In this research, the nickel-iron-silicon carbide multilayer coating is deposited from a single bath with a sulfate composition and by changing the current density between two values (10 and 40 mA/cm2). The number of layers in multilayer coating was 4, 8, 16, 32.The effect of current density and the number of layers on chemical composition, surface morphology, phase structure, corrosion resistance, nano hardness measurement, wear resistance of multilayer coatings respectively using electron... 

Silicon dioxide or silica with the chemical formula SiO2 is the basic component of many minerals. SiO2 films and sheets are widely used in mechanics, optics and electronics due to their outstanding mechanical and electronic performance. The main reason for research in the field of materials with negative Poisson's ratio is their unusual properties, which arise due to the inherent property of negative Poisson's ratio. In this research, the mechanical properties of four two-dimensional silica structures at a temperature of one Kelvin were investigated with the help of molecular dynamics simulation. Also, the sensitivity of the results to the system size and strain rate was studied, and the... 

Sometimes, some ceramics and metals cannot be produced in an integrated manner; In addition, ceramics, like metals, do not fully benefit from the properties of melting and casting; Therefore, it is necessary to produce this group of parts with other methods such as joining to each other. By using joining methods and technologies, it is possible to make composite materials; Therefore, in this way, the applications of ceramic or metal composites have been increasingly expanded. In many researches, bonding of oxide ceramics such as aluminum oxide to itself as well as carbide ceramics such as silicon carbide to itself have been investigated. In this research, the bonding mechanisms of two types...