Nanofabrication and Characterization for Applications in Biochemistry and Molecular Electronics

Sammanfattning: As man-made structures are made increasingly smaller it becomes possible to conduct measurements on single cells, molecules and eventually atoms. In this thesis prerequisites for making this possible are discussed. The underlying thought is that the structures should be used in biological and organic based applications. The discussion is kept in three domains: fabrication, characterization and applications. Fabrication of small structures is mainly accomplished using standard techniques from the semiconductor industry such as UV-lithography or electron beam lithography. For biological and sensor applications the size is important, not the level of complexity. Therefore, a wider range of fabrication methods is available than for manufacturing integrated circuits. Chemical treatment of surfaces, alternative material systems and small scale metallic etching is presented here. The discussion on characterization is focused on scanning probe microscopy and in particular on scanning force microscopy (SFM). SFM allows atomic or nearly atomic resolution on non-conducting samples. In addition it gives a material dependent contrast. This has had a large impact in the bioscience field. The resulting images are deceptively convincing and show in great detail the sample surface as well as mappings of specific force interactions. On the other hand the critical evaluation of images has not had as large a development as the acquiring of images themselves. Artifacts arise due to the finite size of the tip and the rotation of the tip during acquisition. In the thesis examples of artifacts are presented and the effects of the tip and the cantilever on the geometry will be discussed. It is found that for patches which present higher friction, the twisting of the cantilever will contribute to a larger apparent width in the image. By miniaturizing electrode structures, quantitative improvements on sensor structures is the result as well as qualitatively new phenomena. Many of the effects relevant to sensor technology is discussed in the thesis. The standard techniques from the semiconductor industry cannot be directly transferred to biochemical applications or molecular electronics. The material selection is very important. Here some examples of the use of silicon electrodes as well as nanostructured surfaces will be presented.