Controlled synthesis and characterization of some one-dimensional semiconductor nanomaterials

Abstract

Controlled synthesis of one-dimensional semiconductor nanostructures has attracted much attention in recent several years because of its well-controlled size, phase purity, peculiar properties and much more possibility in application fields. In this thesis, we report on the synthesis of well-aligned ZnO nanowire arrays and ZnO nanoribbons on silicon substrate using a horizontal double-tube system, the microstructure characterization and property measurement, even the difference and relation on growth mechanism between nanowires and nanoribbons. In addition, high quality CdS, Ga2O3, In2O3, ZnSe and ZnS nanoribbons in large quantity have been synthesized successfully in a controlled two-step thermal evaporation method. The microstructures and properties of CdS and Ga2O3 have also been reported in details. Horizontal double-tube system is an upgraded structure to single-tube system for better reactive vapor controlled synthesis of nanostructure materials. One small quartz tube with source materials at the bottom is inserted into the original horizontal quartz or alumina tube and located at the central heating position of furnace. Such a structure can conduct a local balance and steady state to reactive vapor environment, leading to a high vapor pressure above the substrate for high nucleation density. Thus the nanowires are confined to grow vertically and form well-aligned arrays. Finely adjusting the heating temperature and carrier gas components, nanoribbons are also available. Through the comparative analysis, it is found that oxygen plays quite an important role in modulating nanowire and nanoribbon growth. 80% oxygen ratio in carrier gas and 80 sccm oxygen flow rate will enhance [10ī0] direction growth to get nanoribbon structure with one rough side. Two-step control thermal evaporation method is quite an effective one to synthesize high quality semiconductor nanoribbons in large quantity. The widths of different produced nanoribbons using such a method are all in μm magnitude, thus it is much easier to handle and manipulate for property measurement on a single nanoribbon than on a single nanowire with diameter in nm magnitude. The optical gain in the PL measurement of CdS nanoribbon is observed. To the best of our knowledge, this is the first evidence of lasing activity in CdS nanoribbons. It is also noted that the pressure, the temperature and the component ratio of carrier gas inside the tube had important influences on the formation of nanoribbons, which provide understanding and support for further investigation on better controlled synthesis of 1D semiconductor nanostructures.

Date of Award	4 Oct 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Shuit Tong LEE (Supervisor)