skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers

Abstract

Organic photovoltaics (OPVs) offer a promising route to low cost photovoltaic (PV) technology that can be inexpensively manufactured on a large scale for use in power generation and commercial products. Solar power conversion efficiencies of laboratory scale OPV devices have recently reached ~5%; however, projected efficiencies of at least 10% will be required for commercialization. An analogous approach that has arisen recently that can potentially increase efficiencies employs metal oxide semiconductors as the electron acceptor, creating a hybrid organic-inorganic device. This approach offers the advantage that the conduction band of the oxide can be tuned in a systematic way through doping, thus potentially achieving higher photovoltages in the device. Additionally, nanostructures of these materials can be easily grown from precursor solutions, providing a technique to precisely control the nanoscale geometry. This work focuses on using ZnO, which is known to have high electron mobility (>100 cm2/Vs), as the electron acceptor. Nanofibers of ZnO can be grown from precursors such as zinc acetate or zinc nitrate to form arrays of nanofibers into which a conjugated polymer can be intercalated to form a composite PV device. The morphology of the nanofiber array is critical to the performance of the device, but currentmore » methods of nanofiber growth from a flat, polycrystalline nucleation layer allow for little morphological control. To overcome this limitation, we have created ordered arrays of ZnO nucleation sites with controllable size and spacing. Toluene solutions of diblock copolymer micelles with ZnCl2 incorporated into the micellar cores were spin-coated onto glass substrates and etched with an O2 plasma to yield hexagonally ordered arrays of ZnO nanoparticles that functioned as nucleation sites. Changing the concentration of ZnCl2 and the molecular weight and ratio of the diblock copolymer resulted in systematic variation in the size and spacing of the nucleation sites. Thermal anneal treatment provided further modification of the nucleation layer, from which ZnO nanofibers were successfully grown from solution, although at present it is not known if the geometry of the as-grown ZnO nanofibers precisely reflects that of the underlying nucleation layer. This work provides a simple and useful method for potentially controlling the nucleation of ZnO nanofibers to be used in hybrid ZnO/organic nanocomposite PV devices.« less

Authors:
; ;
Publication Date:
Research Org.:
DOESC (USDOE Office of Science (SC) (United States))
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1051810
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Undergraduate Research; Journal Volume: 6
Country of Publication:
United States
Language:
English

Citation Formats

Wang, J., Ginley, D.S., and Shaheen, S. Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers. United States: N. p., 2006. Web.
Wang, J., Ginley, D.S., & Shaheen, S. Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers. United States.
Wang, J., Ginley, D.S., and Shaheen, S. Sun . "Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers". United States. doi:. https://www.osti.gov/servlets/purl/1051810.
@article{osti_1051810,
title = {Ordered Nucleation Sites for the Growth of Zinc Oxide Nanofibers},
author = {Wang, J. and Ginley, D.S. and Shaheen, S.},
abstractNote = {Organic photovoltaics (OPVs) offer a promising route to low cost photovoltaic (PV) technology that can be inexpensively manufactured on a large scale for use in power generation and commercial products. Solar power conversion efficiencies of laboratory scale OPV devices have recently reached ~5%; however, projected efficiencies of at least 10% will be required for commercialization. An analogous approach that has arisen recently that can potentially increase efficiencies employs metal oxide semiconductors as the electron acceptor, creating a hybrid organic-inorganic device. This approach offers the advantage that the conduction band of the oxide can be tuned in a systematic way through doping, thus potentially achieving higher photovoltages in the device. Additionally, nanostructures of these materials can be easily grown from precursor solutions, providing a technique to precisely control the nanoscale geometry. This work focuses on using ZnO, which is known to have high electron mobility (>100 cm2/Vs), as the electron acceptor. Nanofibers of ZnO can be grown from precursors such as zinc acetate or zinc nitrate to form arrays of nanofibers into which a conjugated polymer can be intercalated to form a composite PV device. The morphology of the nanofiber array is critical to the performance of the device, but current methods of nanofiber growth from a flat, polycrystalline nucleation layer allow for little morphological control. To overcome this limitation, we have created ordered arrays of ZnO nucleation sites with controllable size and spacing. Toluene solutions of diblock copolymer micelles with ZnCl2 incorporated into the micellar cores were spin-coated onto glass substrates and etched with an O2 plasma to yield hexagonally ordered arrays of ZnO nanoparticles that functioned as nucleation sites. Changing the concentration of ZnCl2 and the molecular weight and ratio of the diblock copolymer resulted in systematic variation in the size and spacing of the nucleation sites. Thermal anneal treatment provided further modification of the nucleation layer, from which ZnO nanofibers were successfully grown from solution, although at present it is not known if the geometry of the as-grown ZnO nanofibers precisely reflects that of the underlying nucleation layer. This work provides a simple and useful method for potentially controlling the nucleation of ZnO nanofibers to be used in hybrid ZnO/organic nanocomposite PV devices.},
doi = {},
journal = {Journal of Undergraduate Research},
number = ,
volume = 6,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • Cited by 23
  • An approach for the formation of ordered groups of Ge nanoislands (quantum dots, QDs) upon epitaxial growth on the surface of a heterostructure constituted by a Si (100) substrate having preliminarily formed seeds in the form of disk-like SiGe nanomounds is developed. It is found that the observed arrangement of QDs within a group is due to the anisotropic elastic-strain energy distribution on the surface of a SiGe nanomound, namely, to the existence of four local energy minima arranged in an ordered manner along the [100] and [010] directions with respect to the seed center. Multilayer structures with vertically alignedmore » QD groups are grown using the suggested approach. The crystal structure and the elemental composition of the spatially ordered nanostructures are examined by transmission electron microscopy, X-ray diffraction analysis, and Raman spectroscopy.« less
  • The electrodeposition of metals is a complex phenomenon influenced by a number of factors that modify the rates of nucleation and growth and determine the properties of the deposits. In this work the authors study the influence of the zinc chloride (ZnCl{sub 2}) concentration on the zinc nucleation process on glassy carbon, in a KCl electrolyte under conditions close to those employed in commercial acid deposition baths for zinc. The electrochemical study was performed using cyclic voltammetry and potentiostatic current-time transients. The charge-transfer coefficient and the formal potential for ZnCl{sub 2} reduction were evaluated from cyclic voltammetry experiments. The nucleationmore » process was analyzed by comparing the transients obtained with the known dimensionless (i/i{sub m}){sup 2} vs. t/t{sub m} response for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl{sub 2} concentration. Scanning electron microscopy analysis of the deposits shows that the deposits are homogeneous and compact although a change in the morphology is observed as a function of ZnCl{sub 2} concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits.« less
  • In the growth of Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} from mixed powders of Pb-doped Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8+{delta}} and other oxides, it has been discovered that a dense array of hillocks or mesas grow at the interface between a Ag overlay and Pb-doped Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8+{delta}} grains during the ramp up to the reaction temperature. As viewed in an environmental scanning electron microscope, the Ag coated grains develop a texture that looks like {open_quote}{open_quote}chicken pox{close_quote}{close_quote} growing on the grains at about 700{degree}C. These hillocks are about 100 nm across and are spaced at aboutmore » 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurements indicate that the hillocks are a recrystallization of (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub 8+{delta}}, and are definitely not a Pb rich phase. {copyright} {ital 1996 American Institute of Physics.}« less
  • The sequential reactions of trimethylaluminum (TMA) and ammonia have been studied in the 1-Torr pressure regime at 600 K with FTIR (Fourier transform infrared spectroscopy) and XPS (X-ray photoelectron spectroscopy). Transmission FTIR spectra acquired through a silica substrate reveal that extended ammonia exposure can overcome the desporption of ammonia from the methylaluminum:ammonia surface adduct identified previously. This increases the number of reactions between methyl groups and ammonia on adjacent adducts and thereby maximizes the population of bridging amino groups on the surface (Al-NH[sub 2]-Al). The resulting NH[sub 2] species can then react with TMA from an additional exposure to producemore » a new layer of methylaluminum species. Repetitions of these sequencial reactions demonstrate that the respective TMA and ammonia reactions are self-limiting, regenerating active sites suitable for promoting chemisorption of the next precursor for the layer-by-layer growth of aluminum nitride. These studies suggest that in addition to providing transport for the source elements, functional groups that remain chemisorbed on the surface may also be used to enhance the uptake of the next precursor and influence bond directionality during film growth at low temperatures. Although the crystallinity of the aluminim nitride film is expected to be limited by the amorphous nature of the silica substrate, the results from a simple conformational analysis suggest a general rule that can be applied to any substrate; if a concerted reaction between dissimilar functional groups is the only mechanism available for growth, then this mechanism will ultimately limit long-range order in the resulting film. 35 refs., 8 figs.« less