Editorial pubs.acs.org/JPCL
Understanding the Growth of Metal Oxide Nanostructures film formation or growth suppression. This understanding is very useful in the design of experiments for the controlled growth of NWs and other nanostructures. While the last 2 decades have witnessed significant advance in synthesis of various complex nanostructures, controlled growth on the atomic level, especially on a large scale and with high reproducibility, remains a challenging task.15−20 Both better fundamental understanding and improved synthetic or fabrication approaches are needed to accomplish this task. In the meantime, advances in sophisticated characterization techniques with high spatial, temporal, and energy resolution should help the development of both new methodologies and nanomaterials to meet the growing demand of novel materials and systems with improved properties and functionalities.
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etal oxide nanostructures are an important class of nanomaterials with unique properties and useful functionalities that are attractive for a variety of applications ranging from electronics to biomedicine and energy conversion. Salient features of metal oxides nanostructures include abundance and usually high stability. To grow metal oxide nanostructures with desired size, shape, and crystal structure in a controllable manner is a primary goal in nanomaterials research but still presents a major challenge today. Toward this goal, substantial research efforts have been made on both the experimental and theoretical fronts.1−5 In this issue of J. Phys. Chem. Lett., two intriguing Perspectives highlight some recent progress in the study and understanding of important factors that affect the growth of metal oxide nanostructures, such as domain walls, carrier or reactive gas flow, and temperature. In the first Perspective, Seidel provided a brief overview of the effect of domain walls on the structure and functionality of complex oxides and their implications to technological applications (Seidel, J. Domain Walls as Nanoscale Functional Elements. J. Phys. Chem. Lett. 2012, 3, 2905−2909). Emphasis was placed on nanoscale phenomena related to domain walls in complex oxides because domain walls are expected to play a critical role in the design and development of novel materials for applications such as electronics, including ferroelectrics and multiferroics.6−8 For instance, the changes in structure that occur at ferroelectric domain walls can lead to changes in transport behavior, with electrical conductivity either increasing or decreasing depending on the specific materials.9−11 Thus, it is important to understand the effect of and then hopefully to control the domain walls for individual materials in order to improve their properties for specific applications of interest. The relation between domain walls and defects or superconductivity was also reviewed.12,13 In the second Perspective, Menzel and co-workers present an overview of the effect and control of carrier gas flow on the synthesis of ZnO nanowires (NWs) using thermal chemical vapor deposition (CVD) (Menzel, A.; Subannajui, K.; Bakhda, R.; Wang, Y.; Thomann, R.; Zacharias, M. Tuning the Growth Mechanism of Nanowires by Controlled Carrier Gas Modulation in Thermal CVD. J. Phys. Chem. Lett. 2012, 3, 2815−2821). Specifically, key parameters that determine the growth of ZnO NWs were reviewed, and a systematic evaluation of the formation of vapor−solid (VS) and catalystassisted growth formation was given based on investigation of the effect of carrier gas flow (Ar), reaction gas flow (O2), and temperature.14 By comparing nanostructures prepared under different experimental conditions, mapping is presented for the deposition techniques where the different growth morphologies can be readily identified and optimal vapor concentrations can be achieved, leading to the controlled formation of films, VS NWs, catalyst-assisted-grown NWs, and the suppression of nanostructure formation. In particular, the flow of Ar and O2 and the substrate temperature sensitively influence the formation of VS and catalyst-assisted-grown NWs or even © 2012 American Chemical Society
Jin Z. Zhang, Senior Editor
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University of California, Santa Cruz, California
AUTHOR INFORMATION
Notes
Views expressed in this Editorial are those of the author and not necessarily the views of the ACS.
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REFERENCES
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The Journal of Physical Chemistry Letters
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(12) Aird, A.; Salje, E. K. H. Sheet Superconductivity in Twin Walls: Experimental Evidence of WO3−x. J. Phys.: Condens. Matter 1998, 10, L377−L380. (13) Gopalan, V.; Dierolf, V.; Scrymgeour, D. A. Defect-Domain Wall Interactions in Trigonal Ferroelectrics. Annu. Rev. Mater. Res. 2007, 37, 449−489. (14) Menzel, A.; Goldberg, R.; Burshtein, G.; Lumelsky, V.; Subannajui, K.; Zacharias, M.; Lifshitz, Y. Role of Carrier Gas Flow and Species Diffusion in Nanowire Growth from Thermal CVD. J. Phys. Chem. C 2012, 116, 5524−5530. (15) Tian, Z. R. R.; Voigt, J. A.; Liu, J.; McKenzie, B.; McDermott, M. J.; Rodriguez, M. A.; Konishi, H.; Xu, H. F. Complex and Oriented ZnO Nanostructures. Nat. Mater. 2003, 2, 821−826. (16) Lao, C. S.; Liu, J.; Gao, P. X.; Zhang, L. Y.; Davidovic, D.; Tummala, R.; Wang, Z. L. ZnO Nanobelt/Nanowire Schottky Diodes formed by Dielectrophoresis Alignment across Au Electrodes. Nano Lett. 2006, 6, 263−266. (17) Song, J. H.; Wang, X. D.; Liu, J.; Liu, H. B.; Li, Y. L.; Wang, Z. L. Piezoelectric Potential Output from ZnO Nanowire Functionalized with p-Type Oligomer. Nano Lett. 2008, 8, 203−207. (18) Li, Y.; Liu, C. S.; Zou, Y. L. Growth Mechanism and Characterization of ZnO Nano-tubes Synthesized using the Hydrothermal-Etching Method. Chem. Pap. 2009, 63, 698−703. (19) Wei, X. Q.; Li, H. C.; Yuan, C.; Li, Q. H.; Chen, S. X. Preparation of Nano-ZnO Supported on Porous Carbon and the Growth Mechanism. Microporous Mesoporous Mater. 2009, 118, 307− 313. (20) Raj, C. J.; Joshi, R. K.; Varma, K. B. R. Synthesis from Zinc Oxalate, Growth Mechanism and Optical Properties of ZnO Nano/ Micro Structures. Crys. Res. Technol. 2011, 46, 1181−1188.
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