Sharif Digital Repository

The need for integration of electron guns together with thermal considerations of thermionic cathodes has led to design new cold cathode guns based on field emission phenomenon. In first part of this thesis, basic field emission theories, fabrication methods of field emitter arrays, effect of different parameters on the field emission properties of field emitter arrays and applications of these arrays are investigated. After setting up fabrication methods of nano-tip field emitters, in the second part of thesis, Si nano-tips and Si field emitter arrays are fabricated using of thermal oxidation of silicon substrate, lithography, and chemical etching of silicon oxide and silicon substrate. Si... 

Nowadays, nanotechnology has emerged in many processes; hence the construction of this scale is also important. By reducing the size of equipment, raw material consumption is reduced and less space is needed for equipment. In addition it is economical. LIGA method has the potential to make parts with small dimensions and accurate tolerances, that it is impossible with other methods (chemical vapor deposition, physical vapor deposition, bulk micromachining, surface Machining). It is possible to assemble the pieces by producing micro-molding in LIGA procedure.In this thesis, numerical simulation of electrodeposition that is one of the main steps in the LIGA procedure has been investigated. One... 

Due to tremendous growth in usage of electron beams in different applications like VLSI, welding, chemical processes, Polymer industry and medical applications, precise study of these beams is of great importance. One of the most important parameters in studying electron beams characteristics is the phenomenon and effect of space charge. Although in most methods of analyzing electron optical systems, this effect is neglected, however in high density beams, this effect is bold. Space charge effect is due to interaction and electrostatic repulsion force between each of the electrons in the beam, which results in a change in shape and also divergence of beam. It is worth to mention that in... 

Today, in order to reach atomic scale resolution, novel nanolithography methods, known as unconventional nanolithography, have been presented, since conventional methods, including photolithography and scanning beam lithography are fundamentally unable to fulfill this need. In this work, a specific type of unconventional lithography, known as scanning probe lithography, is presented. Scanning probe lithography takes advantage of the interactions between a very sharp probe and the sample in nanoscale distances to control this distance, and hence enable the modification of the sample using this sharp probe. In mechanical scanning probe lithography, the probe is used mechanically to change the... 

Carbon nanotubes, due to their extraordinary electronic and physical properties, have attracted much attention in the last decade. Some of their potential applications are in CNT-field effect transistor, field emission devices, physical and chemical sensors, micro and Nanoelectromechanical systems and Nano antenna. In this thesis, we have first reviewed some features of carbon nanotubes and the advantages of PECVD method compared with thermal CVD. In the second part the role of some of the materials (such as H2/NH3/C2H4) in CNT growth are studied. We created a square pattern on the silicon wafer by photolithography. Afterwards, titanium and nickel deposition is done on the mentioned pattern.... 

Various applications of nanostructures in electronics, optoelectronics, MEMS, photonics and plasmonic make their fabrication an interesting research topic recently. Progress in nanotechnology depends on the capability to fabricate, position and interconnect nanometer-scale structures. The development of fabrication devices with nanoscales is mainly dependent on the existence of a suitable nanolithography approach. Patterning materials with nanoscale features aimed at improving integration and device performance faced several challenges. The limitation of conventional lithography systems including resolution related issues, operational costs and lack of flexibility to pattern organic and... 

In many microfluidic devices, focusing particles into a narrow stream is usually an essential step prior to counting, detecting, and sorting them. By installation of microfluidic laboratory functions on a rotating disk, new devices called Lab-on-a-disks, which have plenty of advantages in comparison to ordinary Lab-on-a-chips, shape. In this study, to the best of our knowledge for the first time, a Lab-on-a-disk device is designed and fabricated in order to focus particles prior to detecting them by a conventional CD-ROM as a strong optical system. Hydrophoresis method, using slanted obstacles to induce transverse pressure gradients, is utilized to focus particles. In this regard, the... 

According to today’s medicine progress, the need for improving the medical facilities have been increased. Within the human body, the biomolecules concentration gradient is regulating the cell functions. Biological processes such as immune response, wound healing, and cancer metastasis have been affected by the bimolecular concentration gradient. So understanding the cell behavior in the presence of a chemical gradient can improve the understanding from these biological processes, and also would help in medical researches. On the other hand, finding the appropriate dose of the drugs and in some cases finding the most effective drug is a clinical challenge that made a new field of research in... 

In this research we focus on fabrication, characterization and performance of biosensors based on vertically aligned carbon nanotubes. Carbon nanotubes have been used as high density carbon nanotubes and nanoelectrode array. Carbon nanotubes have been grown using plasma enhanced chemical vapor deposition method. Characterization and performance of biosensors have been studied by cyclic voltammetry and electrochemical impedance spectroscopy methods.
The mediator-less glutamate biosensor is prepared based on covalently attached glutamate dehydrogenase on vertically aligned carbon nanotubes. The biosensor has a low detection limit of 57 nM, two linear range of 0.1-20 µM with sensitivity of...