Highlights

Micro- and Nano-crystals with Novel Shapes

Scientific Achievement

We have achieved synthesizing and characterizing various mesoscale crystals with controlled shapes with both chemical and physical methods, as presented in the viewgraph of this highlight which include images of mesocrystals and nano-contacting.  The major accomplishment during the past years is the development of a novel approach to synthesize charge density wave (CDW) material NbSe₃ in the form of nanowires and converted them into superconducting nanostructures. NbSe₃ nanostructures are prepared by direct reaction of stoichiometric amount of niobium and selenium powders in an evacuated quartz tube at 700C.  Then, superconducting NbSe₂ and NbN nanostructures were synthesized by conversion of NbSe₃ nanostructure precursors into NbSe₂ and NbN, while preserving the morphology of NbSe₃ nanostructures. Magnetization measurements of NbSe₂ and NbN nanostructures show critical temperatures up to 7.2K and 11K respectively.  Morphological characterizations were conducted by scanning electron microscopy.  Transport measurements were conducted on individual nanowires and nanoribbons to study the physical properties affected by reduced dimensions.

We observed intriguing magnetoresistance oscillations and voltage steps at higher driving currents in synthesized NbSe₂ and NbN nanostructures.

Significance

Mesocrystals including both micro- and nanocrystals play important roles in many different areas.  For examples, superconducting and ferromagnetic mesocrystals serve as model systems to experimentally probe quantum confinement on superconductivity and magnetism.  Mesocrystals of noble metals and semiconductors showed high potential for use in nanoscale catalysis, biological labeling, photonic and optoelectronics.  The intrinsic properties of a mesocrystal are determined by its size and shape.  Shape-controlled growth of mesocrystals is one of the most attractive subjects in the current nanoscale research.  Both the understanding of growth mechanisms and the ability to fabricate various types of mesocrystals with novel shapes, however, remains an important goal of modern materials chemistry.  These synthesized crystals provided novel platforms for pursuing new phenomena at the mesoscale.

The developed conversion approach can be directly applied to change the physical properties of other existing compound nanostructures, enabling significant expansion of the availability of nanostructures with desired functions for potential applications.

The principal investigator has been invited to give two talks at international workshops on nanoscale superconductors in Chicago and China and one compact course on nanomaterials in Germany.

Performers