engleski

The Imaging and Analysis of Semiconductor Nanowires by a Combined TEM-AFM Technique.

Using a supercritical fluid technique (SCF), single crystal orientated nanowires of silicon and other semiconductors can be grown by decomposition of organic precursors (e.g. silanes). Using ordered mesoporous silica as a host matrix the SCF methods can be used so as to achieve a 3D ordered matrix of nanowires. Control of the mesoporous structure and pore size allows the diameter of the wires to be ‘tuned’ between 3 and 20 nm allowing control of band structure and thus the electronic properties. The preparation of these embedded nanowires arrays may have significant importance in the development of new computer process architectures. Analysis of these systems is difficult by conventional techniques. Electron microscopy of these materials is strongly dependent on preparation to facilitate dispersion etc. and the formation of representative samples. Electrical characterisation is often dependent on systems where contacts are made by metal evaporation or ‘chance’ linkage between contacts pre-deposited onto a substrate. The TEM-STM technique provides means to carry out both microscopic and electrical measurements. Briefly, this apparatus consists of two AFM tips (one of which is moveable to allow sample position control) between which sits a sample. The assembly is placed into a conventional TEM. The AFM assembly allows selective positioning of the sample for TEM analysis and also allows 3D imaging if required. The two AFM tips allow electrical contact to be made with parts of the sample (e.g. the end of a nanowire) and current voltage data to be collected. Further, force and strength measurements can also be made. One important point of this novel technique is that it is the only technique that allows microscopic analysis of electrical contacts to be made during electrical characterisation. Recent results from nanowire samples prepared by this group are given in this paper.

Nanowires ; Mesoporous ; Imaging ; AFM ; TEM

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