Nanowires are high aspect-ratio crystals with a nanoscale diameter. In the last decade, they have opened new perspectives in many fields including biotechnology, sensing, energy harvesting, electronics and optoelectronics. This is the result of their very particular morphology, their small size, high aspect ratio and high surface-to-volume ratio. Their morphology also renders semiconducting nanowires extremely sensitive to surface states, which can be both an advantage (e.g., for sensing) or a disadvantage (e.g., for solar cells and transistors). This tutorial aims at reviewing some of the basic characterization techniques of semiconductor nanowires and providing the basic understanding that opens new avenues for the application in pioneering applications.
In the first part of the tutorial, techniques used for the characterization of the surface properties of nanowires will be explained. This introductory lecture will be followed by two lectures that will explain in detail what properties enable nanowires to contribute in novel applications with the particular emphasis in next generation of electronic devices and solar cells. The two courses will contain technical information and numerous key examples.
Surface Science Analysis Applied to Nanowires
Surface analysis of nanowires is inherently difficult as most surface science techniques have been designed to address “infinite” flat 2D surfaces. However, with some clever sample design and dedicated measurement strategies it is possible to use most surface common analysis methods also on nanowires. As a result, it is possible to measure nanowire surface geometry, chemistry and electronic properties down to the atomic scale. As examples, I will show how scanning probe and photoelectron spectroscopies/microscopies can be used for detailed surface analysis of nanowires, even during device operation. An emphasis will be on explaining the strategies that enable you to use most surface science tools for studies of high aspect ratio nanostructures and devices at the highest possible performance levels.
2:30 pm BREAK
Characterization of Surface and Interface States in Nanowires and Application to Electronic Devices
Paul C. McIntyre
Using Nanowires in Novel Device Concepts in Photovoltaics
Semiconductor nanowires (NWs) are promising building blocks for next-generation solar energy conversion at low cost. NW ensembles constitute a new class of metamaterial. While the photonic properties of small dielectric structures have been widely studied within the framework of Mie scattering, coupling to poorly confined waveguided modes drives the absorption spectrum in NWs. This tutorial session describes how vertical NWs interact with light. We will show the theoretical and experimental methods to investigate these properties. Based on the special light–matter interactions in NWs, we discuss completely new designs of solar cells that are not possible in the bulk form.
- Anders Mikkelsen, Lund University
- Paul C. McIntyre, Stanford University
- Esther Alarcón-Lladó, AMOLF