8 Matching Results

Search Results

Advanced search parameters have been applied.
in creator/contributor: "Zheng, Haimei"  
Results: 1 - 8
open access

Independent control of the shape and composition of ionic nanocrystals through sequential cation exchange reactions

Description: Size- and shape-controlled nanocrystal growth is intensely researched for applications including electro-optic, catalytic, and medical devices. Chemical transformations such as cation exchange overcome the limitation of traditional colloidal synthesis, where the nanocrystal shape often reflects the inherent symmetry of the underlying lattice. Here we show that nanocrystals, with established synthetic protocols for high monodispersity, can be templates for independent composition control. Specif… more
Date: July 6, 2009
Creator: Luther, Joseph Matthew; Zheng, Haimei; Sadtler, Bryce & Alivisatos, A. Paul
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Hetero-Epitaxial Anion Exchange Yields Single-Crystalline Hollow Nanoparticles

Description: Anion exchange with S was performed on ZnO colloidal nanoparticles. The resulting hollow ZnS nanoparticles are crystal whose shape is dictated by the initial ZnO. Crystallographic and elemental analyses provide insight into the mechanism of the anion exchange.
Date: August 26, 2009
Creator: Park, Jungwon; Zheng, Haimei; Jun, Young-wook & Alivisatos, A. Paul
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Photovoltaic Devices Employing Ternary PbSxSe1-x Nanocrystals

Description: We report solar cells based on highly confined nanocrystals of the ternary compound PbSxSe1-x. Crystalline, monodisperse alloyed nanocrystals are obtained using a one-pot, hot injection reaction. Rutherford back scattering and energy filtered transmission electron microscopy suggest that the S and Se anions are uniformly distributed in the alloy nanoparticles. Photovoltaic devices made using ternary nanoparticles are more efficient than either pure PbS or pure PbSe based nanocrystal devices.
Date: February 5, 2009
Creator: Ma, Wanli; Luther, Joseph; Zheng, Haimei; Wu, Yue & Alivisatos, A. Paul
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Nanocrystal Diffusion in a Liquid Thin Film Observed by in situ Transmission Electron Microscopy

Description: We have directly observed motion of inorganic nanoparticles during fluid evaporation using a Transmission Electron Microscope. Tracking real-time diffusion of both spherical (5-15 nm) and rod-shaped (5x10 nm) gold nanocrystals in a thin-film of water-15percentglycerol reveals complex movements, such as rolling motions coupled to large-step movements and macroscopic violations of the Stokes-Einstein relation for diffusion. As drying patches form during the final stages of evaporation, particle m… more
Date: April 17, 2009
Creator: Zheng, Haimei; Claridge, Shelley A.; Minor, Andrew M.; Alivisatos, A. Paul & Dahmen, Ulrich
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Sulfidation of Cadmium at the Nanoscale

Description: We investigate the evolution of structures that result when spherical Cd nanoparticles of a few hundred nanometers in diameter react with dissolved molecular sulfur species in solution to form hollow CdS. Over a wide range of temperatures and concentrations, we find that rapid Cd diffusion through the growing CdS shell localizes the reaction front at the outermost CdS/S interface, leading to hollow particles when all the Cd is consumed. When we examine partially reacted particles, we find that … more
Date: May 22, 2008
Creator: Cabot, Andreu; Smith, Rachel; Yin, Yadong; Zheng, Haimei; Reinhard, Bjorn; Liu, Haitao et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Direct observation of two-step crystallization in nanoparticle superlattice formation

Description: Direct imaging of nanoparticle solutions by liquid phase transmission electron microscopy has enabled unique in-situ studies of nanoparticle motion and growth. In the present work, we report on real-time formation of two-dimensional nanoparticle arrays in the very low diffusive limit, where nanoparticles are mainly driven by capillary forces and solvent fluctuations. We find that superlattice formation appears to be segregated into multiple regimes. Initially, the solvent front drags the nanopa… more
Date: October 6, 2011
Creator: Park, Jungwon; Zheng, Haimei; Lee, Won Chul; Geissler, Phillip L.; Rabani, Eran & Alivisatos, A. Paul
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Selective Facet Reactivity During Cation Exchange in Cadmium Sulfide Nanorods

Description: The partial transformation of ionic nanocrystals through cation exchange has been used to synthesize nanocrystal heterostructures. We demonstrate that 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. In the case of copper I (Cu+) cation exchange in cadmium sulfide (CdS) nanorods, the reaction starts preferentially at the ends of the nanorods such that copper sul… more
Date: December 18, 2008
Creator: Sadtler, Bryce; Demchenko, Denis; Zheng, Haimei; Hughes, Steven; Merkle, Maxwell; Dahmen, Ulrich et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
open access

Direct Observation of Room-Temperature Polar Ordering in Colloidal GeTe Nanocrystals

Description: Ferroelectrics and other materials that exhibit spontaneous polar ordering have demonstrated immense promise for applications ranging from non-volatile memories to microelectromechanical systems. However, experimental evidence of polar ordering and effective synthetic strategies for accessing these materials are lacking for low-dimensional nanomaterials. Here, we demonstrate the synthesis of size-controlled nanocrystals of the polar material germanium telluride (GeTe) using colloidal chemistry … more
Date: December 7, 2009
Creator: Polking, Mark J.; Zheng, Haimei; Urban, Jeffrey J.; Milliron, Delia J.; Chan, Emory; Caldwell, Marissa A. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
Back to Top of Screen