טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentBashouti Mohammed
SubjectSynthesis and Physical Characterization of Semiconductor
Nanocrystals with Anisotropic Shape
DepartmentDepartment of Chemistry
Supervisor Professor Efrat Lifshitz
Full Thesis textFull thesis text - English Version


Abstract

In recent years, there has been an increase of interest in the scientific and technological aspects of anisotropic structures including nanowires (NWs). These materials exhibit unique chemical and physical properties. The special properties are associated with two important characteristics: (1) the quantum size effect (QSE) and (2) the existence of a relatively large fraction of atoms at the surface of each nanocrystal (NC).  These effects alter the electronic properties of NCs by splitting the bulk energy bands into discrete states, shifting these transitions to higher energies. The lead chalcogenides in IV-VI semiconductor materials, in particular, are of special interest due to their optical activity in the near IR spectra regime. These NCs have bulk energy-gaps, (Eg), of 0.29 eV and of 0.41 eV for PbSe and PbS, respectively, and large Bohr radius (aB) of 46 nm and 18 nm for PbSe and PbS, respectively.  Thus, the unique physical properties, making them useful for various optical and telecommunication applications. The ultimate goal of the proposed research is concerned with the synthesis and physical characterization of PbSe and PbS semiconductor NCs that have an anisotropic shape. This document proposes the development of a simple colloidal method of preparation of PbSe and PbS NCs at low temperatures (10¾190°C), with bidentate surfactants such as ehtylenediamine (en) and ethyleneglycol (eg), at various time durations and concentrations under inert atmosphere. The research focused on the following issues, according to the steps as listed below:  

·        Development of anisotropic shape of PbS and PbSe NCs: The dependence of colloidal synthesis on the varying concentration of the bidentate surfactant (en) and (eg) for example, temperature, reaction time duration and under inert conditions, led to a controlled width and length, surface quality, and uniformity of PbS and PbSe NCs and uniform surface quality.

·        Physical characterization of prepared semiconductor nanowires (PbSe and CdS) and and PbSe NCs arrays:  The research included the investigation of their morphological, optical and electrical characterization. The electrical measurement of a single PbSe wire-like assembly revealed a conductivity of 7.0 Ω-1cm-1. The emission spectra of the aligned CdS NWs showed a linear polarization, which is important for polarized-light sources in high-resolution detection of polarized light or in other optical elements in the visible and near-IR spectral regime.