Oriented attachment can generate wide range of nanomaterials with unusual morphologies, and is typically driven by reducing their surface energy during crystal growth (1). However, it is not completely understood why anisotropic nanostructures can be formed via oriented attachment when they lacks anisotropic crystal symmetry, as shown in examples of nanowires, nanorods, and nanosheets of lead (Pb) chalcogenide (2-4). So far, inhomogeneous surface dipole or soft template formation of surfactant molecules has been discusses as a key role in oriented attachment of those examples; but it is yet still challenging to achieve precise control over size and shape of Pb chalcogenide nanostructures, which is important to control their carrier dynamics and charge transport (5).

Here we will discuss our recent development on 1D and 2D nanostructures of Pb chalcogenides. Chemical engineering of crystal growth in Pb chalcogenide allows rational control of their morphology and composition, which also tailors their optical and electrical properties. Especially due to the large Bohr radius (PbS 18 nm, PbSe 46 nm) and narrow band gap (PbS 0.41 eV, PbSe 0.28 eV) of Pb chalcogenides (6), the above mentioned Pb chalcogenide nanostructures exhibit the effect of quantum confinement of carriers. We will explore how asymmetric confinement of carrier is manifested in the characteristics of charge carriers, exciton dynamics, and other optoelectric properties for these Pb chalcogenide nanostructures based on theoretical and spectroscopy studies. Furthermore, there are huge opportunities of Pb chalcogenide nanostructures in photovoltaics, sensors, transistors and other optoelectronic devices. We will discuss how the unique properties of anisotropic nanostructures can be utilized for those applications.

References:

1. H. Zhang, J. F. Banfield, Energy Calculations Predict Nanoparticle Attachment Orientations and Asymmetric Crystal Formation. The Journal of Physical Chemistry Letters 3, 2882 (2012).

2. K.-S. Cho, D. V. Talapin, W. Gaschler, C. B. Murray, Designing PbSe Nanowires and Nanorings through Oriented Attachment of Nanoparticles. J. Am. Chem. Soc. 127, 7140 (2005).

3. W.-k. Koh, A. C. Bartnik, F. W. Wise, C. B. Murray, Synthesis of Monodisperse PbSe Nanorods: A Case for Oriented Attachment. J. Am. Chem. Soc. 132, 3909 (2010).

4. C. Schliehe et al., Ultrathin PbS Sheets by Two-Dimensional Oriented Attachment. Science 329, 550 (2010).

5. L. A. Padilha et al., Carrier Multiplication in Semiconductor Nanocrystals: Influence of Size, Shape, and Composition. Accounts of Chemical Research 46, 1261 (2013).

6. I. Kang, F. W. Wise, Electronic structure and optical properties of PbS and PbSe quantum dots. J. Opt. Soc. Am. B 14, 1632 (1997).

Weon-kyu Koh

Los Alamos National Lab

Appearances