A study of the vibration characteristics of a deoxyguanosine molecule and a deoxyadenosine molecule bonded onto the
surface of silicon is presented. The vibrations of the systems can be classified into five modes: nonlocal vibrational
modes, local vibrational modes, quasi-local modes, backbone vibrational modes and molecular bond vibrational modes.
The general separation of the molecular bond modes (i.e., which occur in the infrared region) and other vibrational
modes (i.e., which occur in the far-infrared (Far-IR) region) is only weakly influenced by mounting the molecules onto
the surface of silicon through linker molecules. The main influence of the binding of the molecule onto to the surface of
a silicon substrate is the shifting of the vibrational modes towards the terahertz regime (i.e., ~ 100 cm-1) and an
associated increase of the number of these low frequency modes. Furthermore, the FAR-IR active vibrational regions
(i.e., defined where there exists the strongest absorption peaks) are in the range of 300 cm-1 to 1903 cm-1 for a
deoxyguanosine molecule and 500 cm-1 to 1841 cm-1 for a deoxyadenosine molecule, respectively. For frequencies
below these Far-IR regions, the absorption intensity is small. However, the vibrations in this region are almost all nonlocal
vibration modes which are important for the study of interaction between bases and for the development of
sequence information of DNA molecules in terms of optical techniques.
The traditional implementation of resonant tunneling diodes (RTD) as a high-frequency power source always requires the utilization of negative-differential resistance (NDR). However, there are inherent problems associated with effectively utilizing the two-terminal NDR gain to achieve significant levels of output power. This paper will present a new design methodology where resonant tunneling structures (RTS) are engineered to exhibit electronic instabilities within the positive-differential-resistance (PDR) region. As will be demonstrated, this approach utilizes a microscopic instability that alleviates the need to reduce device area (and therefore output power) in an effort to achieve low-frequency stabilization.
Resonant tunneling diodes (RTDs) are ultra-small semiconductor devices that have potential as very high frequency oscillators. To describe the electron transport within these devices, the Wigner-Poisson Equations are used. These equations incorporate quantum mechanics to describe how the electron distribution changes in time due to kinetic energy, potential energy, and scattering effects. To study the RTD, we apply numerical continuation methods to calculate the steady-state electron distribution as the voltage difference across the RTD varies. To implement the continuation methods, the RTD simulator is interfaced to LOCA (Library of Continuation Algorithm), a software library that is a part of Sandia National Laboratories' parallel solver package, Trilinos. With more sophisticated numerical solvers, we are able to calculate solutions on finer grids that were previously too computationally intensive. This is very important to allow for detailed studies of correlation effects which may dramatically influence oscillatory behavior in RTD-based devices. The more accurate results derived from this work reveal new physical effects that were absent in prior studies. Hence, these physics-based and more refined numerical simulations will provide new insights and greatly facilitate the future optimization of RTD-based oscillator sources and thus has important relevance to THz-frequency-regime based spectroscopic sensing technology.