Synthesis, Characterisation and Device Application of Silicon Nanoparticles produced by Mechanical Attrition

Odo, Ayodele

Synthesis, Characterisation and Device Application of Silicon Nanoparticles produced by Mechanical Attrition

Doctoral Thesis

2009

Publisher

University of Cape Town

Department

Department of Physics

Faculty

Faculty of Science

Abstract

Nanostructured silicon is a promising materials for research because it serves as building blocks for nanotechnological applications, such as nano and quantum electronics, sensors and energy applications. However, many of the synthesis methods come with an increased level of sophistication, and thus the unit cost of material produced is high. The study shows that cheap and mass production of silicon nanoparticles can be achieved e ciently with a topdown process of mechanical attrition, particularly using an orbital pulveriser. The inclusion of the powder in a polymeric binder resulted in a new class of nanocomposite whose electrical properties are promising for devise applications using simple printing processes. Scanning and transmission electron microscopy studies reveal that the powders consist of a wide range of size and shape distribution, with large faceted particles with sizes between 1 ô 3 m and relatively small particles of sizes 40ô100nm. The variation of the average particle size with milling time ts well with a rst order exponential decay model which was used to evaluate the limiting particle size as about 120nm. The structural properties of the nanocomposites was investigated using small angle X-ray scattering, while the electrical properties were investigated by conducting I ô V measurements on a metal-nanocomposite-metal structure. Further tests for electronic properties like eld e ect mobilities were achieved by using the nanocomposite as the active layer in an insulated gate eld e ect transistor structure. Electrical characterisation reveals that the carrier injection and transport is determined by two main factors: the concentration of particles constituting the composite, and the level of external bias voltage on the structure. The nanocomposite systems show a clear percolation threshold for charge conduction. Below the percolation threshold, transport is mainly limited by the matrix or insulating binding medium. Direct tunneling and eld emission (FE) are the major transport mechanism for all concentrations at low voltages, while thermally activated processes, such as hopping and thermionic emission are major contributors at low concentrations. At higher concentrations and eld, Poole-Frenkel and Richardson-Schottky conduction mechanisms, resulting from barrier limiting process in the interface, of the metal contact to an interfacial insulator is dominant. Similar pronounced contribution from space charge limited current process resulting from accumulation of charges at the interface, and traps in the bulk, is pronounced at concentrations above the percolation threshold. The transistors function as ambipolar devices, where the dominance of either carrier is deteri mined by the sign and swing direction of the gate potential. The best transistors fabricated have a hole mobility of 2:63 10ô5cm2=V s and electron mobility 7:81 10ô7cm2=V s.

Keywords

Physics

Reference:

Collections

PhD / Doctoral

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