We previously predicted a semimetal-semiconductor transition in bismuth nanowires as a function of nanowire diameter due to quantum confinement effects, and we have now succeeded in observing this effect through transport measurements. We have devised a way to prepare arrays of aligned bismuth nanowires down to 7 nm diameter (embedded in an anodic alumina template), 50-100 microns in length, with a wire density of ~ 1011/cm2, with their wire axes along a common crystalline orientation, and preserving the crystal structure of bulk bismuth. Raman spectroscopy potentially provides a convenient way to characterize nanotubes for their (n, m) indices, in a manner that is compatible with the measurement of other nanotube properties, such as transport, mechanical and electronic properties at the single nanotube level, and the dependence of these properties on nanotube diameter and chirality. The (n, m) assignments made to individual carbon nanotubes are corroborated by measuring the characteristics of other features in the Raman spectra that are sensitive to nanotube diameter and chirality. The high sensitivity of the Raman spectra to diameter and chirality, particularly for the characteristics of the radial breathing mode, which are also uniquely related to the same (n, m) indices, thereby providing a structural determination of (n, m) at the single nanotube level. Of particular importance is the uniqueness of the electronic transition energies for each nanotube, which are described in terms of two integers (n, m) which uniquely specify the geometrical structure of the nanotube, including its diameter and chirality. However, at the single nanotube level, the characteristics of each feature can be studied in detail, including its dependence on diameter, chirality, laser excitation energy and closeness to resonance with electronic transitions. All Raman features normally observed in single wall nanotube (SWNT) bundles are also observed in spectra at the single nanotube level, including the radial breathing mode, the G-band, the D-band and the G’-band. This work eventually led to the observation of Raman spectra from one single nanotube, with intensities under good resonance conditions comparable to that from the silicon substrate, even though the ratio of carbon to silicon atoms in the light beam was approximately only one carbon atom to one hundred million silicon atoms. Next we showed characteristic differences between the Raman profile of the G-band depending on whether the nanotubes were metallic or semiconducting. at the University of Kentucky in 1997) of the Raman spectra from bundles of single wall carbon nanotubes and showing a strong enhancement of the spectra through a diameter selective resonance Raman effect. This work started in earnest with the initial observation (with Rao et al. Regarding carbon nanotubes, which were previously predicted to be either semiconducting or metallic depending on their geometries, we have been developing the method of Raman spectroscopy as a sensitive tool for the characterization of single wall carbon nanotubes, one atomic layer in wall thickness. Recent research activities in the Dresselhaus group that have attracted wide attention are in the areas of carbon nanotubes, bismuth nanowires and low dimensional thermoelectricty. Pappalardo Fellowships show submenu for “Pappalardo Fellowships”.Astrophysics Observation, Instrumentation, and Experiment.Research Areas show submenu for “Research Areas”.Mentoring Programs Information show submenu for “Mentoring Programs Information”. PhD in Physics, Statistics, and Data Science.For Graduate Students show submenu for “For Graduate Students”.For Undergraduate Students show submenu for “For Undergraduate Students”.Academic Programs show submenu for “Academic Programs”.Administration show submenu for “Administration”.
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