Hybrid Organo-Molecular / Silicon Electronics

2nd NSF NIRT: Our newest project investigating attachment of organic molecules on silicon surfaces as a means of controlling doping and introducing new forms of hybrid quantum conduction. I serve as PI on this project working with Professors Avik Ghosh (ECE), Lloyd Harriott (ECE), Lin Pu (Chemistry) and Keith Williams (Physics).

DARPA MOLEapps: Our second molecular electronics project aimed at developing the fundamental molecular electronic devices and circuits to serve as the building blocks of a future microprocessor. UVA leads a multi-university including team now including professors Lloyd Harriott, Mircea Stan, Nathan Swami, Avik Ghosh and myself at UVA, Mark Reed at Yale University, Jim Tour at Rice University, and Paul Franzon at North Carolina State University. Our ultimate goal is to develop devices based on organic molecules bonded directly to crystalline silicon. Device characteristics will be modeled by Ghosh as my group uses new molecules developed by Tour in a UHV vapor phase process for self-limiting single layer molecular assembly on silicon. Devices will be processed Swami and critically tested by Reed. Harriott will then drive the fabrication of circuits based on the architectural ideas of Stan and Franzon. Selected publications:

"Vapor Phase Deposition of OPE Molecules for use in Molecular Electronic Devices"

"The Effects of Molecular Environments on the Electrical Switching with Memory of Nitro Molecules"

"Nanowell Device For The Electrical Characterization Of Metal-Molecule-Metal Junctions"

"Study of the Room Temperature Molecular Memory Observed from a Nanowell Device"

Guided Quantum Dot Self-Assembly

In systems such as GeSi on Si strained layer epitaxy, quantum dot sized islands can form. Strain fields tend to separate islands and they can begin to assemble into 2D arrays. However, the strain forces are short range and so, while two or three or four islands may grow in a nice row, the ordering tends to deteriorate as rows and arrays get larger. One solution is to just take over from nature and artificially carve a dot pattern using a patterning tool such as lithography, or focused ion beam milling, or AFM manipulation. This works - but it is so slow and/or expensive that it would be impossible to fabricate a commercially complex quantum dot circuit in this manner. Guided self-assembly is our idea of a middle path: Use a focused ion beam to quickly add or subtract only a few atoms at each site. Then grow islands under conditions where they tend to nucleate on these minutely perturbed sites. That is, guide (very subtly) nature towards self-assembling dots where we need them to form the circuit.

"Conditions for self-assembly of quantum fortresses and analysis of their possible use as quantum cellular automata"

"Growth of Quantum Fortress Structures in Si 1-xGe x /Si via Combinatorial Deposition"

UVA Virtual Electronics Lab

As science and engineering expand, students confront a growing list of specialized courses. They are told these courses offer skills needed to meet scientific and technological challenges.- but may not be given the opportunity to apply these skills until their final undergraduate years. Many students are frustrated by the absence of early "hands-on" experience. Others cannot see how early challenging courses will ever "come together," and therefore leave science and engineering for "easier" alternatives. A solution is to provide these students with examples of how introductory materials fit into larger technological endeavors. Microelectronics is already part of every student's world, lurking inside almost every electronic device. It exploits leading edge developments in almost every field of science and engineering. It thus offers the student superb illustrations on the value of their studies if it can be presented in a form accessible to the younger student.

This NSF funded project is developing materials that provide a "Gateway" into physics-based electronics technologies for high school science students, university freshman facing the choice of majors, or curious members of the general public. UVA leads a team that includes the Northern Virginia Community College System, the State University of New York - Buffalo, a Virginia magnet high school of science and technology, and local Albemarle County high schools. By exploiting leading edge developments in 3D Web-based modeling, the team is developing "Virtual experiments" that will provide students with visual representations of microelectronics devices and processes. Pages are being rapidly added to the freely-accessible (commercial free) website. Each page includes up to two dozen interactive animations along with plain English explanations. Current pages include: High-school experiments on magnetic induction and electrostatic attraction/repulsion; Approximately two-dozen pages on elementary electronics circuits (involving batteries, capacitors and resistors) along with corresponding water flow analogies (a battery becomes a gerbil powered water wheel); How a semiconductor crystal is made and used to from a transistor; How an integrated circuit is made; A university microelectronics lab; A virtual tour of a real life commercial integrated circuit plant; Virtual scientific instruments including scanning electron microscopes SEM), atomic force and scanning tunneling microscopes (AFM/STM) and molecular beam epitaxy crystal growers (MBE)

"The Creation of Microelectronics-based Visualizations to Enhance Science Education and Literacy"

Link to the UVA Virtual Lab website: www.virlab.virginia.edu

NSF NUE: Hands-on Introduction to Nanoscience

Our NSF sponsored effort to develop an hands-on introduction to nanoscience for early undergraduates of all majors. The class's subtitle of "We're Not in Kansas Anymore!" emphasizes the need to show students that at the nanoscale the familiar rules of Newtonian physics no longer apply as the weirdness of quantum mechanics takes its place. In the lab students will make use of miniaturized atomic force and scanning tunneling microscopes. To understand their operation, these instruments have been fully disassembled and explained in virtual reality in webpages on the UVA Virtual Lab website (above). I serve as PI, working with Keith Williams, Avik Ghosh, Lloyd Harriott and Nathan Swami. All class materials are being posted on the class's public website for full use by other educators.

Link to the "Hands-on Introduction to Nanoscience" class homepage

Earlier Projects:

1st NIRT Project on Molecular Electronics

Our first project on molecular electronics funded under the NSF NIRT (Nanoscience Interdisciplinary Research Team) initiative. This project brings together computer engineers (Prof. Mircea Stan and James H. Aylor), with microelectronics fabricators (Prof. Lloyd Harriott and myself), with a chemist (Prof. Lin Pu) and a chemical engineer (Prof. Matt Neurock). The aim is to find a path to integrating molecular based electronics devices with traditional solid state transistors to form complex yet practical hybrid integrated circuits. Selected publications:

Molecular Level Printing / Nanoprinting

Advances microelectronics have been fueled largely by photolithography, the light-based process through which patterns are transferred to metals and semiconductors. To make things smaller, the wavelength of the light used has now been shrunk to the point that it no longer passes through focusing glass lenses. The short term-solution has been to use more exotic and difficult!) lens materials. The longer-term solution will require adoption of radically different lithographies based on electrons, ions, or X-rays. These will almost certainly add hugely to the complexity of factories, which already cost upwards of 5 billion dollars!! DARPA (again) challenged researchers to propose out-of-the-box alternatives that might either circumvent this complexity (for at least selected applications) or loosen constraints in current technology (e.g. the requirement for near perfectly planar surfaces). Our UVA-based team collaborated with teams at Harvard, Princeton and the Naval Research Laboratory to investigate several possible approaches based on "nanoprinting" - a sort of microscale rubber stamping. Within the UVA team, the Bean Group had responsibility for developing new "printing materials and processes," while other groups focused on developing the nanoprinting-tool

Virtual Integrated Prototyping

This DARPA project exploited advances in computational platforms, applied mathematics and materials physics to provide some of the first realistic simulations of thin film growth. In the third generation of this project, DARPA challenged modelers to team with leaders in thin film growth, deposition tool vendors and corporate end-users, to radically advance selected materials and devices. Our team, including Princeton, UVA, ion-beam tool vendor CVC Commonwealth Scientific, and end-user Honeywell Microelectronics, targeted new memory devices based on GMR ("gigantic magnetoresistive") devices. In the Bean Group, we interacted with modelers to identify the key atom-scale characteristics of growing films. We then turned to basic science to identify in-situ sensors that might capture such real-time information. Having chosen in-situ ellipsometry, ion beam scattering, and optical scattering as those tools, we rolled up our sleeves to develop prototype commercial sensors to work within the evolving Commonwealth / Honeywell deposition system design.

NSF Focused Research Group

Study of the competition between three dimensional growth effects and dislocation formation in the growth of strained layer materials. This project involved a collaboration with the group Joe Greene of the University of Illinois.

NSF Materials Research Science and Engineering Center (MRSEC) on Nanoscopic Material Design

Beginning of our studies of "guided self-assembly" (see above).