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Atomic Scale Characterization and Fabrication

Summary:

This research is focused on developing new metrology and fabrication methods with atomic-scale precision. The experimental research emphasizes the design of custom instrumentation intended to push the frontiers of nanoscale measurement. Using state of the art scanning probe techniques, a diverse set of research areas are being explored, including future electronics and spintronics, atom manipulation, epitaxial growth of materials, correlation of microstructure and magnetism and electronic properties of nanostructures.

Recent work has focused on measurements of two material systems, graphene and the dilute magnetic semiconductors Mn/GaAs and Mn/InAs. Graphene is a single sheet of carbon that holds potential for future electronic material applications because of its low scattering rates and high carrier mobilities.

We are developing atomic scale measurements to characterize graphene grown on SiC substrates in collaboration with the research groups of Professors Phillip First and Walter de Heer at the Georgia Institute of Technology. This work utilizes our ultra-stable cryogenic scanning probe system to obtain detailed spatial maps of the scattering patterns from defects in the graphene lattice. These maps show for the first time how defects lead to scattering in graphene that would otherwise be forbidden by conservation of the material’s newly discovered pseudo-spin degree of freedom.

Mn in III-V semiconductors is a dilute magnetic semiconductor that holds potential in spintronic applications. Understanding the role of the substitutional Mn in the III-V host is critical to achieve higher Curie temperatures. We are developing measurements to characterize and manipulate single Mn impurities on III-V surfaces in order to gain a better understanding of the electronic properties. The STM probe tip has been successfully used to induce an adsorbed Mn atom to substitute for a lattice In atom, thereby becoming magnetically active. The process has been characterized as a function of tunneling voltage and current, and is being modeled in collaboration with Dr. Steven Erwin at the Naval Research Laboratory.

 

Accomplishments:

  • Imaged the interface beneath epitaxial graphene on SiC and measured scattering interference patterns from defects in the graphene.
  • Developed non-linear control algorithms for atomically precise motion of plezo-electric actuators.
  • Completed an autonomous atom assembler for perfect nanostructure fabrication.
  • Used atom manipulation techniques to substitute single magnetic impurities into a semiconductor lattice and to fabricate molecular lattices on metal surfaces with intentional defects that mimic photonic band gaps in photonic crystals.
  • Developed a unique ultra-low temperature (10mK) scanning probe instrument for the study of the quantum electronic properties of nanostructures.
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 STM topographic image, 20 nm x 20 nm, of a single layer of graphene grown on SiC.
 STM topographic image, 20 nm x 20 nm, of a single layer of graphene grown on SiC. The image shows a combination of the graphene lattice and the underlying SiC surface reconstruction, visible because the graphene is “semi-transparent” under these imaging conditions. This transparency allows structural aspects of the buried interface to be discerned.


Contact

Joseph Stroscio, Phone 301-975-3716

NIST
100 Bureau Drive, MS 6202
Gaithersburg, MD 20899-6202