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Hierarchical Materials Synthesis

Applications: lasers, photovoltaics, sensors, novel logic devices

New bottom-up approaches to crystal growth enable the realization of complex heterostructured materials with useful functions built-in during synthesis. Current research efforts focus on the atomic layer deposition (ALD) of 2D materials and chemical vapor deposition of 1D nanowires with complex morphologies such as regular kinking.

 Kinked Nanowire Growth

Complex morphologies including regular kinking can be induced in nanowires  by modulation of growth conditions. Facet selective etching of kinked nanowires, combined with atom probe tomography, reveals facet selective doping.

Z Sun, D. N. Seidman, and L. J. Lauhon, "Nanowire Kinking Modulates Doping Profiles by Reshaping the Liquid-Solid Growth Interface" Nano Letters. 17 (7), 4518-4525 (2017)

ALD of 2D Materials

ALD provides exceptional control of nucleation selectivity and dimensions at the sub-nanometer scale. The anisotropic bonding in van der Waals crystals presents challenges for uniform film growth but provides opportunities for bottom-up synthesis.

III-V Nanowires on Silicon

Collaborators in the group of Gregor Koblmüller at the Technical University of Munich grow (In,Ga,Al)-As nanowires directly on Si substrates by Molecular Beam Epitaxy. The large lattice mismatch between III-Vs and Si is mitigated by the small spatial footprint of the nanowires. Direct monolithic growth can allow for nanowire emitters and photodetectors to be integrated with current CMOS technology as on-chip optical links. Characterization of the structure, strain, and composition of these nanowires by the Lauhon group is crucial for the development of growth processes and efficient nanowire optics.

Additional References

  • Mårtensson, Thomas, et al. "Epitaxial III− V nanowires on silicon." Nano Letters 4.10 (2004): 1987-1990.
  • Tomioka, Katsuhiro, et al. "III–V nanowires on Si substrate: selective-area growth and device applications." IEEE Journal of Selected Topics in Quantum Electronics 17.4 (2011): 1112-1129.