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Báo cáo sinh học: " This peer-reviewed article was published immediately upon acceptance. It can be downloaded, printed "Nanoscale Research Letters This Provisional PDF corresponds to the article as it appeared upon acceptance. Fully formatted PDF and full text (HTML) versions will be made available soon. Critical aspects of substrate nanopatterning for the ordered growth of GaN nanocolumns Nanoscale Research Letters 2011, 6:632 doi:10.1186/1556-276X-6-632 Francesca Barbagini (fbarbagini@isom.upm.es) Ana Bengoechea-Encabo (abengo@isom.upm.es) Steven Albert (salbert@isom.upm.es) Javier Martinez (jmartinez@isom.upm.es) Miguel Angel Sanchez-Garcia (sanchez@isom.upm.es) Achim Trampert (trampert@pdi-berlin.de) Enrique Calleja (calleja@die.upm.es) ISSN 1556-276X Article type Nano Express Submission date 24 August 2011 Acceptance date 14 December 2011 Publication date 14 December 2011 Article URL http://www.nanoscalereslett.com/content/6/1/632 This peer-reviewed article was published immediately upon acceptance. It can be downloaded, printed and distributed freely for any purposes (see copyright notice below). Articles in Nanoscale Research Letters are listed in PubMed and archived at PubMed Central. For information about publishing your research in Nanoscale Research Letters go to http://www.nanoscalereslett.com/authors/instructions/ For information about other SpringerOpen publications go to http://www.springeropen.com © 2011 Barbagini et al. ; licensee Springer.This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Critical aspects of substrate nanopatterning for the ordered growthof GaN nanocolumnsFrancesca Barbagini*†1, Ana Bengoechea-Encabo†1, Steven Albert†1, JavierMartinez†1, Miguel Angel Sanchez García†1, Achim Trampert†2, and Enrique Calleja†11 ISOM and Electrical Engineering Dept. (DIE), Escuela Técnica Superior deIngenieros de Telecomunicaciónes (ETSIT), Universidad Politécnica de Madrid s/n,Madrid, 28040, Spain2 Paul Drude Institut für Festköperelektronik, Hausvogteiplatz 5-7, Berlin, 10117,Germany*Corresponding author: fbarbagini@isom.upm.es† Contributed equallyEmail addresses:FB: fbarbagini@isom.upm.esABE: abengo@isom.upm.esSA: salbert@isom.upm.esJM: javier.martinez@isom.upm.esMASG: sanchez@isom.upm.esAT: trampert@pdi-berlin.deEC: calleja@die.upm.es -1-Abstract Precise and reproducible surface nanopatterning is the key for a successfulordered growth of GaN nanocolumns. In this work, we point out the maintechnological issues related to the patterning process, mainly surface roughness andcleaning, and mask adhesion to the substrate. We found that each of these factors,process-related, has a dramatic impact on the subsequent selective growth of thecolumns inside the patterned holes. We compare the performance of e-beamlithography, colloidal lithography, and focused ion beam in the fabrication of hole-patterned masks for ordered columnar growth. These results are applicable to theordered growth of nanocolumns of different materials.Keywords: GaN nanocolumns; ordered growth; molecular beam epitaxy; surfacecleaning; roughness; adhesion; e-beam lithography; colloidal lithography; focused ionbeam.Background The unique properties of III-nitride nanocolumns [NCs] in contrast to thin filmstructures derive from the reduced footprint on the substrate that enables essentiallydislocation- and strain- free growth on a variety of substrates [1]. Defect-free NCsexhibit excellent electronic transport and optical properties for the fabrication of high-efficiency optoelectronic nanodevices, such as photodetectors, light-emitting diodes,and solar cells [2-5]. Moreover, the controlled coalescence of III-nitride NCs wouldlead to strain-free pseudosubstrates with reduced defect densities [6]. During the past years, III-nitride NCs have been grown in the self-assembledmode by plasma-assisted molecular beam epitaxy [PA-MBE] [7-9] on varioussubstrates. However, fluctuations in density and dimensions of the NCs lead tosignificant dispersion in the optoelectronic properties and render the deviceprocessing very difficult. Thus, the realization of true devices relies on theachievement of ordered arrays of homogeneous NCs by localization of the epitaxialgrowth on predetermined preferential sites. This growth mode is known as selectivearea growth [SAG], and it has attracted much scientific interest in the last few years[10-15]. In the SAG, the substrate is pre-patterned with a mask of nanoholes. The NCsnucleate and grow selectively inside the nanoholes and not on the surface of the mask.Many experimental works have been reported on the SAG of GaN/InGaNnanocolumnar heterostructures [10-14]. In these works, the hole patterning of themask material was achieved either by focused ion beam [FIB] ...