Abstracts Category : Other

Near-field raman spectroscopy of single-walled carbonnanotubes

by Neil Anderson

Because of diffraction, propagating radiationcannot be localized to dimensions smaller than half the opticalwavelength and hinders a comprehensive analysis of the structural,vibrational and electronic properties of materials with sizedimensions below one hundred nanometers. To overcome this limit, ananoscale optical antenna is used to localize radiation tolength-scales much smaller than the wavelength of light. By placinga laser-irradiated optical antenna, such as a bare gold tip, a fewnanometers above a sample surface, (i.e. into the samplesnear-field), an optical interaction between the confined field andsample is used to induce a spectroscopic response within aninteraction volume of (20 nm). My doctoral research has revealedhow both phonons and excitons are confined in low-dimensionalstructures. By using near-field optical spectroscopy vibrationalmodes characteristic of individual single-walled carbon nanotubes(SWNTs) have been mapped with ultra-high spatial resolution. Mywork has shown that vibrational modes in SWNTs can be localized toregions of 20 nm. In addition, it is shown that the out-of-planevibrational modes experience greater Raman enhancement compared toin-plane vibrational modes in SWNTs. By combining near-field Ramanand near-field photoluminescence measurements it is have shown thatexcitons are localized to defect-rich regions in semiconductingSWNTs, revealing that bright optical emission in SWNTs originatesfrom bound excitons. Furthermore, it is demonstrated that thequantum efficiency in SWNTs can be increased by over two orders ofmagnitude using laser-irradiated gold tips. Finally, near-fieldRaman microscopy was applied to investigate structures buriedbeneath a capping layer with nanoscale (30 nm)resolution.