טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRaz Ofer
SubjectElectrochemical Behavior of Silicon in Room Temperature
Ionic Liquids
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Yair Ein-Eli
Full Thesis textFull thesis text - English Version


Abstract

RTIL’s (Room Temperature Ionic Liquids) are a new class of compounds that has emerged in the last two decades. These compounds are usually made of an organic cation, and inorganic or organic anion.  Their properties include: very low vapor pressure, low melting temperature (<100oC), thermal stability over a wide temperature range (300-400oC). RTIL’s also possess a wide electrochemical window, making them an attractive medium to conduct electrochemical processes.

Our research is aimed of characterization of the electrochemical behavior of silicon in RTIL, determining the effect of the RTIL composition (anion and cation type). Our study reports on the formation of Porous silicon (PS) by application of a positive potential on n-type silicon without illumination and its mechanism. PS were formed in 1-ethyl-3-methyl-imidazolium oligo fluorohydrogenate (EMI(HF)2.3F) room-temperature ionic liquid (RTIL). This RTIL was selected since it is highly conductive and acidic. The results indicate that EMI(HF)2.3F may serve as a non-aqueous electrolyte equivalent to hydrofluoric acid, allowing the formation of pores under anodic polarization. A detailed mechanism suggests that the formation of the porous silicon is based on concentration of Si-F bonds which leads to a strong electric field at local spots on the silicon surface. The study also showed that the porous silicon structure is altered significantly under different polarizations and durations.

Furthermore, electrodeposition of metallic ruthenium thin film (<10nm), which generates a great interest was conducted from IL's.  Such a thin film can serve as an Adhesion Promoter and Diffusion Barrier (APDB) between silicon and copper in microelectronic and nanroelectronic applications. Ruthenium electrodeposition on    n-Si and Au from RTIL is conducted by dissolving RuCl3 salt in 1-methyl-3-butyl imadizolium hexaflourophosphate or 1-methyl-3-butyl dicyanamide RTIL's followed by cathodic potential application. Ruthenium electrodeposition mechanism emerged from in-situ STM studies. It is shown that the electrodeposition mechanism and surface morphology is influenced significantly by the ionic liquid composition, purity and temperature.