NANOSCIENCE & TECHNOLOGY

Research in physics, chemistry, life sciences, and information technologies is converging upon a commonality: understanding materials at the nanometer scale. Recent advances in material engineering at the atomic level fostered discoveries of new materials with fascinating properties which created enormous potential for a new Industrial Revolution: nanotechnology. The promise of nanotechnology can only be realized, however, if researchers learn to understand and utilize the special rules that control the behavior of materials at the nanoscale.

Our research program covers several major areas in nanoscience, namely nanoscale superconductors, nanowires, semiconductor spintronics, and novel quantum materials for hydrogen storage.
 

Nanoscale superconductors:
A key requirement for making functional nano-devices is the ability to acquire perfect control of their structure and morphology. One promising avenue to accomplish this is to exploit quantum mechanical laws while tuning and assembling nanostructures. We recently demonstrated how quantum confinement of itinerant electrons can be utilized to engineer the two-dimensional morphology of thin Pb films and PbBi quantum alloys to create atomically smooth, highly crystalline thin film superconductors. The extraordinary morphology has allowed for the first observation of a remarkably robust superconductive critical state where even the thinnest films (five atom layers) can support macroscopic circulating super-currents with absolutely minimal dissipative flow, emphasizing the crucial role of “quantum trapped vortices."

Atom wires:
The "bottom-up" approach to nanoelectronics aims to use molecules or even single atoms as basic building blocks for electronic structures and devices. Interconnects consisting of "atomic wires" can already be fabricated in the laboratory but their electrical properties will likely be very exotic. In our laboratory, we investigate the electronic properties of atomic wires or arrays of wires on semiconductor templates, using a variety of surface analysis techniques. Our interests are mainly fundamental and are aimed at understanding their exotic electronic properties in relation to atomic structure. Specific topics include structural relaxations, phase transitions, charge- and spin density waves, spin-charge separation, localization, and electrical transport.

Spintronics:
Spin-electronics or spintronics has become a vibrant area in semiconductor research in recent years and is likely to impact our lives in a way that reminds us of the early days of the transistor and microelectronics industry. It promises, among other things, electronic devices that are smaller, faster, and less-power consuming which could ultimately lead to a new revolution in the microelectronics and information technology. Unlike current microelectronic devices, spintronic devices utilize both “spin” and charge of electrons to carry or store information. Spin is an intrinsic quantum mechanical property of the electrons that are flowing through the circuit. Its discovery dates back to 1925 and it has been known for a very long time that spin is intimately related to magnetism. Very recently, researchers began learning how to utilize this spin property in electronic materials. It requires integration of semiconductors and magnetism.

We initiated a new research program on silicon-compatible magnetic semiconductors. The objective is to transform conventional silicon, germanium, and their alloys into magnetic materials by incorporating magnetic impurities (“dopants”) using specialized growth techniques such as Molecular Beam Epitaxy (MBE). If silicon and germanium can be made ferromagnetic (like iron and nickel, for instance) or, if high-quality films of these materials can be grown “epitaxially” on top of a magnetic metal, then one can exploit the electron spins in the magnet to inject a spin current into a silicon device. In principle, this would enable logic operations utilizing the electron spin rather than its charge, as is done in conventional electronics.

Novel quantum materials for hydrogen storage:
One of the main obstacles to replacing fossil fuels with hydrogen is the lack of a light-weight storage material that can absorb and release substantial amounts of hydrogen under or near ambient conditions. This obstacle could potentially be alleviated or even removed if only one could control the thermodynamic and kinetic parameters of hydrogen adsorption on solid surfaces independent of the surface structure and chemical composition. Recent observations of quantum size effects and oscillatory chemical reactivity of ultrathin metal films, originating from the quantum confinement of conduction electrons inside the film, is an exciting and major development because it allows for additional control and in-depth understanding of thickness-dependent reactivity. Its physical origin appears to be related to the oscillatory pattern of the charge spilling above the metal surface, associated with the standing electron waves normal to the metal surface. We are exploring the fundamental underpinnings for hydrogen adsorption, dissociation, absorption, diffusion, and recombination on quantum-mechanically confined films and alloys of light metal elements. Our goal is to obtain atomic- and molecular-level understanding of the physical and chemical processes involved in hydrogen adsorption, storage, and release in novel quantum confined materials; and development of precise quantum control of hydrogen storage and release. Fundamental understanding and thorough investigation of these quantum phenomena and their potential for tuning chemical processes are directly relevant to the use of light-metal hydrides as storage media for hydrogen.

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