Jack Chan

Investigation of Gd3N@C2n (40 n 44) family by Raman and inelastic electron tunneling spectroscopy

The structure and vibrational spectrum of Gd3N@C80 is studied through Raman and inelastic electron tunneling spectroscopy as well as density-functional theory and universal force eld calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd3N-C80 bond which reduces the ideal icosahedral symmetry of the C80 cage. The vibrational modes involving the movement of the encapsulated species are a ngerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the Gd3N@C2n 40 n 44 family as well as Y3N@C80, Lu3N@C80, and Y3N@C88 for comparison. Conductance measurements have been performed on Gd3N@C80 and reveal a Kondo effect similar to that observed in C60.

Raman study of Fano interference in p-type doped silicon

As the silicon industry continues to push the limits of device dimensions, tools such as Raman spectroscopy are ideal to analyze and characterize the doped silicon channels. The effect of inter-valence band transitions on the zone center optical phonon in heavily p-type doped silicon is studied by Raman spectroscopy for a wide range of excitation wavelengths extending from the red (632.8 nm) into the ultra-violet (325 nm). The asymmetry in the one-phonon Raman lineshape is attributed to a Fano interference involving the overlap of a continuum of electronic excitations with a discrete phonon state. We identify a transition above and below the one-dimensional critical point (E = 3.4 eV) in the electronic excitation spectrum of silicon. The relationship between the anisotropic silicon band structure and the penetration depth is discussed in the context of possible device applications. Copyright

Noise analysis of carbon nanotube field effect transistors irradiated by electron beam

Using current noise measurement techniques, the authors have studied the effects of electron beam exposure on field effect transistors based on carbon nanotube channels. In the case of p-type semiconducting nanotubes, the authors find that high doses induce a potential barrier along the channel, and transport is dominated by the tunneling events across this barrier. The authors suggest that the barrier is induced by charges trapped in the underlying SiO2 barrier. Complementary studies on metallic nanotubes do not exhibit this behavior.

Transport in carbon nanotube field-effect transistors tuned using low energy electron beam exposure

We have studied the effect of low energy (30 keV) electron beam exposure on carbon nanotube field-effect transistors, using an electron beam lithography system to provide spatially controlled dosage. We show that reversible tuning of the transport behavior is possible when a backgate potential is applied during exposure. n-type behavior can be obtained by electron beam exposure of a device with positive gate bias, while ambipolar behavior can be obtained via negative gate bias. The observed transport behavior is relatively stable in time. We propose possible mechanisms for the observed phenomena and suggest directions for further research.

Electron Beam Induced Two-State Noise in Carbon Nanotubes

Discrete current switching is induced in carbon nanotubes by electron beam irradiation. Switching amplitudes of 3% to 6% are observed at room temperature. Switching is created by electron beam exposure with dosage as low as 1000 pC/cm. Relative switching amplitude remains constant as the bias voltage varies, suggesting that current fluctuation is dominated by mobility fluctuation. Changes in the noise power spectral density following electron beam exposure will be discussed.