Building Structural Complexity in Semiconductor Nanocrystals through Chemical Transformations

Thesis/Dissertation · Fri May 01 00:00:00 EDT 2009

DOI:https://doi.org/10.2172/970575· OSTI ID:970575

Sadtler, Bryce F ^[1]

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1. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Methods are presented for synthesizing nanocrystal heterostructures comprised of two semiconductor materials epitaxially attached within individual nanostructures. The chemical transformation of cation exchange, where the cations within the lattice of an ionic nanocrystal are replaced with a different metal ion species, is used to alter the chemical composition at specific regions ofa nanocrystal. Partial cation exchange was performed in cadmium sulfide (CdS) nanorods of well-defined size and shape to examine the spatial organization of materials within the resulting nanocrystal heterostructures. The selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. The exchange of copper (I) (Cu⁺) cations in CdS nanorods occurs preferentially at the ends of the nanorods. Theoretical modeling of epitaxial attachments between different facets of CdS and Cu₂S indicate that the selectivity for cation exchange at the ends of the nanorods is a result of the low formation energy of the interfaces produced. During silver (I) (Ag⁺) cation exchange in CdS nanorods, non-selective nucleation of silver sulfide (Ag₂S), followed by partial phase segregation leads to significant changes in the spatial arrangement of CdS and Ag₂S regions at the exchange reaction proceeds through the nanocrystal. A well-ordered striped pattern of alternating CdS and Ag₂S segments is found at intermediate fractions of exchange. The forces mediating this spontaneous process are a combination of Ostwald ripening to reduce the interfacial area along with a strain-induced repulsive interaction between Ag₂S segments. To elucidate why Cu⁺ and Ag⁺ cation exchange with CdS nanorods produce different morphologies, models for epitaxial attachments between various facets of CdS with Cu₂S or Ag₂S lattices were used to calculate interface formation energies. The formation energies indicate the favorability for interface nucleation at different facets of the nanorod and the stability of the interfaces during growth of the secondary material (Cu₂S or Ag₂S) within the CdS nanocrystal. The physical properties of the CdS-Ag₂S and CdS-Cu2S binary nanorods are discussed in terms of the electronic structure of their components and the heterostructure morphology.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 970575
• Report Number(s): LBNL-2028E; TRN: US201002%%1285
• Resource Relation: Related Information: Designation of Academic Dissertation: doctoral; Academic Degree: PhD; Name of Academic Institution: University of California, Berkeley; Location of Academic Institution: Berkeley, CA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
CADMIUM SULFIDES
CATIONS
CHEMICAL COMPOSITION
COPPER
ELECTRONIC STRUCTURE
MORPHOLOGY
NANOSTRUCTURES
NUCLEATION
PHYSICAL PROPERTIES
RIPENING
SEGREGATION
SEMICONDUCTOR MATERIALS
SHAPE
SILVER
SILVER SULFIDES
STABILITY
TRANSFORMATIONS
nanoscience
nanocrystals
semiconductor heterostructures
complexity