A label-free DNA hybridization detector using carbon nanotube transistor arrays is developed. The sensors are
comprised of a network of carbon nanotubes covered by thin oxide layer, which serve as efficient charge transducers for
biomolecules in solution. Probe DNA sequences are immobilized on the gate oxide, and the conductance is measured
before and after exposure and hybridization with a target DNA. Complementary binding results in a net charge doubling
at the oxide surface which induces a positive shift in the threshold voltage and concomitant increase in the current at
fixed bias. The method does not involve chemical functionalization of the carbon nanotubes and is compatible with
protocols in conventional DNA microarrays. Most importantly, the technique does not require reporter molecules or
tagging labels, which greatly simplifies the operation and reduces the cost. We have shown a measurable response to
hybridization with target concentration of ~1 nM. The implementation, theory of operation, device fabrication and
solutions to pertinent engineering issues to build practical system are discussed.
We investigate the dependence of the photovoltaic characteristics of organic photocells on the relative concentration of the donor-acceptor molecular complex. The devices were fabricated using a new [MEH-PPV] - co - [phenylene vinylene] blend with C<sub>60</sub>. We find that the morphology and device performance are strongly influenced by the molar fraction (x) of C<sub>60</sub> in the electroactive layer of the device. The best device was obtained with x = 0.6 and manifested <i>V</i><sub>OC</sub> = 0.85 V, <i>J</i><sub>SC</sub> = 2.65 mA/cm<sup>2</sup>, <i>FF</i> = 0.42, and <i>η</i><sup>P</sup><sub>ext</sub> = 1%.
This paper discussed the further development of magnetic force microscopy to observe successive changes in recorded marks resulting from heating cycles in the presence of an external field. Our results on a conventional TbFeCo-based medium indicate very stable domains up to relatively high temperatures, which then rapidly collapse once wall movement starts. The images show that due to variations of the media on the local scale, the marks diminish in a highly nonuniformity manner. Inhomogeneities of the magnetic and mechanical properties of the medium play a crucial role in retarding wall motion and lead to formation of complex domain shapes prior to collapse. Pinning at the grooves has been similarly observed. Quantitative analysis of the results provide additonal insights concerning mark size reduction and edge sharpening as a function of temperature. This analysis also leads to the derivation of a critical radius for this media and biasing field combination.
We have developed magnetic force scanning tunneling microscopy as a powerful tool to analyze magnetic patterns on recording media with sub-micron resolution. The technique employs the interaction of surface magnetic fields with a flexible thin-film magnetic probe. We have made a thorough theoretical analysis of the interaction between the probe and the surface magnetic fields emanating from a typical recorded pattern. Quantitative data about the constituent magnetic fields and the underlying magnetization patterns can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic recording: data-density and data overwrite. In the course of these studies we have developed new techniques to analyze the magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.