Yuefei Ma

Scenarios for Molecular-Level Signal Processing

Several research efforts are being carried out in molecular electronics; both theory and experiment claim extraordinary findings for molecular devices. However, before practical molecular circuits can be implemented, we need to develop scenarios for information coding and transfer in molecular circuits able to operate at integration densities and speeds orders of magnitude higher than current ICs do. Initial attempts have been already proposed; however,a simple adaptation to methods being used in current microelectronics devices does not offer much hope at the atomistic and nanoscopic levels due to the large dissipation energy densities that would be generated. We have proposed two new paradigms to process and transmit information in molecular circuits that can defeat the heat dissipation problem. One is based on the characteristic vibrational behavior of molecules and clusters, and the other is based on the molecular electrostatic potentials. It is suggested that these two scenarios can be used for molecular signal processing and transfer in molecular circuits; a theoretical demonstration using computational techniques is presented for these two paradigms.

TERAHERTZ SIGNAL TRANSMISSION IN MOLECULAR SYSTEMS

Terahertz signal transmission in DNA is simulated and analyzed using molecular dynamics and digital signal processing techniques to demonstrate that signals encoded in vibrational movements of hydrogen bonds can travel along the backbone of DNA and eventually be recovered and analyzed using digital signal processing techniques.

Encoding and transport of information in molecular and biomolecular systems

We have proposed possible scenarios based on molecular electrostatic potentials and molecular vibrational modes that can be combined to process and encode information in nanosized circuits. These two intrinsic properties determine how molecules interact or communicate to each other and to themselves. These scenarios may provide the solution to satisfy the urgent need for exponential growth of computational performance and eventually to radically change the way how computation is performed. Presently, the increase in computational power is achieved by scaling down the size of devices. However, already at the nanometer scale, the process of scaling down is seriously limited by physical laws regardless of what materials are used. These limitations lead us to compromise the speed of electronic devices against heat removal, which is one of the consequences of scaling-down. The new scenarios would allow computing with molecules in a molecular friendly fashion and eventually in a way similar to those in biological systems. The molecular potentials and vibronics would indeed address the heating issues, which are the overarching killers at future technology nodes

Molecular-based processing and transfer of information in the terahertz domain for military and security applications

An implementation and review of our recently proposed scenarios [1-13] for processing and transfer of information is presented. We will show how computing using molecular potentials and vibronics communications can be adapted to upgrade present charge-current approaches, which are already in the limits of their technical and perhaps physical limits because their immense heat dissipation problems. It has long been recognized the many advantages and potential payoffs that the development of THz based applications could bring to the military and security areas. We focus our implementation in the development of THz sensing and imaging for a wide range of military and security applications as systems operating at these frequencies have shown to have high sensitivity and selectivity when applied to the analysis of molecules. These are properties that are highly desirable in the design of sensing tools for the detection, identification and characterization of chemical and biological agents; and in the design of monitoring tools for the detection of these substances, both in closed and, with less selectivity, in open environments. Many materials of interest for security applications including explosives, and chemical and biological agents have characteristic THz fingerprints which set them apart from non-hazardous materials, thus allowing their identification. As molecular electronics techniques become available [14], they could sharply improve our present detection and sensing techniques.

Transient behavior at the nanoscale.

Transient and steady state responses of a system to an input are well-known features of materials and systems in science and engineering. These responses depend on the intrinsic parameters of the system and on the nature of the input. We find that a system comprised of nanosized features no longer shows the typical stationary characteristics as their microscopic or solid-state counterparts. Interestingly, because of the chemistry of the nanostructure, thermal motion of the atoms, and external fields, the nanosized system shows extended electrical transient behavior, compatible with highly nonlinear features such a negative differential resistance and hysteresis.

Terahertz molecular electronics devices and systems

Several problems, almost impossible to defeat, among them, heat removal, addressing small devices, and fuzziness at atomistic scales confronts standard CMOS electronics. What we are concluding after intensive research is that the material is not the major problem but the way how we encode information is what can allow us to continue the steady exponential grow in computational power know as the Moores law. Although molecules and nanoclusters are the alternative for scaling down devices, we need to develop scenarios for information coding and transfer in molecular circuits able to operate at integration densities and speeds orders of magnitude higher than in present integrated circuits. A simple scaling down using the same scenarios being used in todays microelectronics devices does not offer much hope at the atomistic and nanoscopic levels. We proposed two scenarios: One is based on the characteristic vibrational behavior of molecules and clusters and the other is based on their molecular electrostatic potentials. It is proposed that these two scenarios can be used for molecular signal processing and transfer in molecular circuits; theoretical demonstrations using computational techniques are presented for these two paradigms. The molecular electrostatic potential in the neighborhood of a molecule has very well defined zones of positive and negative potential that can be manipulated to encode information and vibrational modes of long molecules can allow us to transfer signals. Both scenarios allow very lower energies, higher speeds, and higher integration densities than in any other technology. A review of our search for other scenarios for coding, processing and transport of information is provided.

Chapter 4 Analysis of programmable molecular electronic systems

Publisher Summary Amplitude modulation (AM) and frequency modulation (FM) can be used to transmit information in molecular wires usingmolecular vibrations with a power dissipation of ∼50nW when working at 1 Tbps. These kinds of vibrational movements are at the range of terahertz. The vibrational modes can not only be excited by an electromagnetic wave, but can also be detected using infrared (IR) spectroscopy or Raman spectroscopy if their movements cause changes in the electrostatic dipole (IR active) or in polarizability (Raman active). When the signal is transferred using molecular vibrational modes, the atoms vibrate to a certain position, which may introduce a change in the molecular electrostatic potential (MEP) distribution of the whole molecular system. This change is subsequently transferred through vibronics. Thus, by proper programming, the hundreds of molecules inside the nanocell can be viewed as signal-processing devices. If information is transmitted using vibronics, the power dissipation can be evaluated from the energy that excites and keeps the molecular wire to vibrate.