Browsing by Subject "nanocrystals"

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Depletion-driven assembly of polymer-coated nanocrystals
(2022-09-05) Green, Allison M.; Kadulkar, Sanket; Sherman, Zachary M.; FitzSimons, Thomas M.; Ofosu, Charles K.; Yan, Jiajun; Zhao, David; Ilavsky, Jan; Rosales, Adrienne M.; Helms, Brett A.; Ganesan, Venkat; Truskett, Thomas M.; Milliron, Delia J.
Depletion-driven assembly has been widely studied for micron-sized colloids, but questions remain at the nanoscale where the governing physics are impacted by the stabilizing surface ligands or wrapping polymers, whose length scales are on the same order as those of the colloidal core and the depletant. Here, we probe how wrapping colloidal tin-doped indium oxide nanocrystals with polymers affects their depletion- induced interactions and assembly in solutions of polyethylene glycol. Copolymers of polyacrylic acid grafted with polyethylene oxide provide nanocrystal wrappings with different effective polymer graft densities and molecular weights. (Ultra) small angle X-ray scattering, coarse-grained molecular dynamics simulation, and molecular thermo- dynamic theory were combined to analyze how depletant size and polymer wrapping characteristics affect depletion interactions, structure, and phase behavior. The re- sults show how depletant molecular weight, as well as surface density and molecular weight of polymer grafts, set thresholds for assembly. These signatures are unique to depletion-driven assembly of nanoscale colloids and mirror phase behaviors of grafted nanoparticle–polymer composites. Optical and rheological responses of depletion-driven assemblies of nanocrystals with different polymer shell architectures were probed to learn how their structural differences impact properties. We discuss how these han- dles for depletion-driven assembly at the nanoscale may provide fresh opportunities for designing responsive depletion interactions and dynamically reconfigurable materials.
Dimensionality and Design of Isotropic Interactions that Stabilize Honeycomb, Square, Simple Cubic, and Diamond Lattices
(2014-09) Jain, Avni; Errington, Jeffrey R.; Truskett, Thomas M.; Jain, Avni; Truskett, Thomas M.
We use inverse methods of statistical mechanics and computer simulations to investigate whether an isotropic interaction designed to stabilize a given two-dimensional lattice will also favor an analogous three-dimensional structure, and vice versa. Specifically, we determine the 3D-ordered lattices favored by isotropic potentials optimized to exhibit stable 2D honeycomb (or square) periodic structures, as well as the 2D-ordered structures favored by isotropic interactions designed to stabilize 3D diamond (or simple cubic) lattices. We find a remarkable "transferability" of isotropic potentials designed to stabilize analogous morphologies in 2D and 3D, irrespective of the exact interaction form, and we discuss the basis of this cross-dimensional behavior. Our results suggest that the discovery of interactions that drive assembly into certain 3D periodic structures of interest can be assisted by less computationally intensive optimizations targeting the analogous 2D lattices.
Doping Nanocrystals And The Role Of Quantum Confinement
(2007-09) Chan, T. L.; Tiago, M. L.; Chelikowsky, J. R.; Chan, Tzu‐Liang; Tiago, Murillo L.; Chelikowsky, James R.
Recent progress in developing algorithms for solving the electronic structure problem for nanostructures is illustrated. Key ingredients in this approach include pseudopotentials implemented on a real space grid and the use of density functional theory. This procedure allows one to predict electronic properties for many materials across the nano-regime, i.e., from atoms to nanocrystals of sufficient size to replicate bulk properties. We will illustrate this method for doping silicon nanocrystals with phosphorous.
The First Example of Tb-3-Containing Metallopolymer-Type Hybrid Materials with Efficient and High Color-Purity Green Luminescence
(2015-02) Zhang, Zhao; Feng, Heini; Liu, Lin; Yu, Chao; Lu, Xingqiang; Zhu, Xunjin; Wong, Wai-Kwok; Jones, Richard A.; Pan, Mei; Su, Chengyong; Jones, Richard A.
In the series of homo-leptic trinuclear complexes {[Ln(3)(L)(4)Cl-4(MeOH)(H2O)]center dot Cl} (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) self-assembled from the allyl-modified benzimidazole-type ligand HL (4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol) and LnCl(3)center dot 6H(2)O, a suitable energy level match endows efficient green luminescence (Phi(overall) = 72%) of Tb-3-arrayed complex 3. The copolymerization between each of these complex monomers 1-4 and C=C-containing MMA (methyl methacrylate) or NBE (norbornene) shows that degradative chain transfer of the terminal four flexible allyl groups within restrains their radical polymerization with MMA while it does not hinder their effective ring-opening metathesis polymerization (ROMP) with NBE. Thus, two kinds of PMMA-supported doping hybrid materials 1@PMMA, 2@PMMA, 3@PMMA and 4@PMMA and PNBE-supported metallopolymer-type hybrid materials Poly( NBE-1), Poly(NBE-2), Poly(NBE-3) and Poly(NBE-4) are obtained, respectively. Especially for both 3@PMMA and Poly(NBE-3) with high color-purity characteristic green emission of Tb3+ ions, improved physical properties including significantly enhanced luminescence (Phi(overall) = 76% or 83%) are observed, and covalent-bonding endows a higher-concentration self-quenching as compared to physical doping.
Luminescent CulnSe2-Based Core/Shell Nanocrystals: Characterizing Defects in CulnSe2 Nanocrystals
(2015-05) Sher, Soa-Jin; Korgel, Brian A.
As interest continues to grow in new materials for next-generation photovoltaic (PV) devices (i.e. solar cells), it is important to understand the mechanisms and limitations of promising materials. Many researchers are focused on the use of semiconductor nanocrystals (NCs) in PV devices because of their potential to be deposited in thin films via solution, which is more cost-effective than traditional methods. This study focuses on CuInSe2 (CISe) NCs, which are part of a larger class of materials known as CuInxGa1-xSe2 (CIGS). CIGS is well-known in the PV industry, especially for its use on flexible substrate materials, which have significant cost and processing advantages over traditional, bulky, glass-based solar cells. However, defects within or on the surface of the CIGS NCs limit the movement of holes and electrons, affecting the ability of the NCs to extract charge carriers; these defects ultimately result in lower-efficiency PV devices. The purpose of this study is to better understand the defects within CISe NCs by coating them with ZnS shells. A Zn-based shell was successfully formed around a CISe NC without compromising the integrity of the CISe NC. The shell also successfully passivated the surface defects and increased the efficiency of the CISe NCs. By creating luminescent CISe-based core/shell NCs, this study examines the nature of CISe NC defects and the implications of these defects on the future of CISe in the PV industry.
A Self-Assembling Lanthanide Molecular Nanoparticle for Optical Imaging
(2015-12) Brown, Katherine A.; Yang, Xiaoping; Schipper, Desmond; Hall, Justin W.; Depue, Lauren J.; Gnanam, Annie J.; Arambula, Jonathan F.; Jones, Jessica N.; Swaminathan, Jagannath; Dieye, Yakhya; Vadivelu, Jamuna; Chandler, Don J.; Marcotte, Edward M.; Sessler, Jonathan L.; Ehrlich, Lauren I. R.; Jones, Richard A.; Brown, Katherine A.; Schipper, Desmond; Hall, Justin W.; Depue, Lauren J.; Gnanam, Annie J.; Arambula, Jonathan F.; Sessler, Jonathan L.; Jones, Richard A.
Chromophores that incorporate f-block elements have considerable potential for use in bioimaging applications because of their advantageous photophysical properties compared to organic dye, which are currently widely used. We are developing new classes of lanthanide-based self-assembling molecular nanoparticles as reporters for imaging and as multi-functional nanoprobes or nanosensors for use with biological samples. One class of these materials, which we call lanthanide "nano-drums", are homogeneous 4d-4f clusters approximately 25 to 30 angstrom in diameter. These are capable of emitting from the visible to near-infrared wavelengths. Here, we present the synthesis, crystal structure, photophysical properties and comparative cytotoxicity data for a 32 metal Eu-Cd nano-drum [Eu8Cd24L12(OAc)(48)] (1). We also explored the imaging capabilities of this nano-drum using epifluorescence, TIRF, and two-photon microscopy platforms.