טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYuval Shmueli
SubjectElectrospinning and Characterization of PZT and Ga/ZnO
Nanofibers
DepartmentDepartment of Chemical Engineering
Supervisors Full Professor Grader Gideon
Dr. Shter Gennady
Full Thesis textFull thesis text - English Version


Abstract

Nanofibers are one-dimensional nanostructures that are characterized by unique geometrical properties of large surface to volume ratio and large aspect ratio of length to diameter. These properties make the one-dimensional nanostructures excellent candidates for many applications in the fields of micro and nano electronics, optoelectronics, electromechanical, electrochemical and solar cells.

Electrospinning is an efficient and low cost technique for nanofibers preparation. This technique is based on uniaxial elongation of a viscoelastic solution under a high voltage. The high voltage creates two forces - one is strong electric field between the charged solution droplet and the grounded counter electrode while the second is repulsion between electric charges on the droplet surface. These forces cause stretching of the solution into fibers with diameters that range from several microns to tens of nanometers. Preparation of ceramic nanofibers via this technique requires the addition of inorganic precursors into the electrospun solution. Moreover, thermal treatment of the raw fibers (called green fibers), is required to burnout the organic components and sintering the inorganic part into a ceramic fiber.

In this work we synthesized nanofibers of gallium doped zinc oxide (Ga-ZnO) and lead zirconate titanate (PZT) by electrospinning. The first step of the work is the preparation of the solutions for the electrospinning process. In this step the appropriate precursors had to be chosen. The second step is the electrospinning. In this step the influence of many parameters was examined. These parameters were working voltage, distance between the needle electrode and the collector and feed rate of the solution. Then, after obtaining as-prepared ("green") fibers, thermal treatments had to be conducted. These thermal treatments included first step in low temperatures for evaporating residual solvents and second step at high temperatures for organics burnout and sintering. The high temperatures thermal treatments were followed by many experiments, intensive investigation and thermal analysis of the materials. As a consequence, optimal thermal treatments were carried to find the optimal temperatures, durations and surrounding atmospheres.

After synthesis, the fibers were characterized by x-ray diffraction, high resolution scanning electron microscopy and specific surface area according to B.E.T absorption isotherm. Electrical behavior and humidity sensing properties were examined for gallium doped zinc oxide single nanofibers assembled on special micro device.