© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 3786 www.advmat.de www.MaterialsViews.com COMMUNICATION wileyonlinelibrary.com Adv. Mater. 2011, 23, 3786–3790 Suenne Kim,* Yaser Bastani, Haidong Lu, William P. King, Seth Marder, Kenneth H. Sandhage, Alexei Gruverman, Elisa Riedo, and Nazanin Bassiri-Gharb* Direct Fabrication of Arbitrary-Shaped Ferroelectric Nanostructures on Plastic, Glass, and Silicon Substrates Ferroelectric (FE) materials represent one of the most versatile smart materials for use at the nanometer scale owing to their unique properties of switchable spontaneous polarization, pyro- electricity, and piezoelectricity. Specifically, the perovskite-based FEs show a very high piezoelectric response, up to an order of magnitude higher than non-ferroelectric compositions such as AlN and ZnO. [1] Such high electromechanical coupling makes ferroelectrics great candidates for sensor, actuator, and energy harvesting devices, especially on small scales in micro- and nano-electromechanical systems (MEMS/NEMS). While the processing of FE thin films (both epitaxial and polycrystalline) has been extensively examined and developed over the last few decades , [1] robust techniques that do not require epitaxial substrates for the patterning of 2D and 3D FE nanostructures remain elusive. Processing techniques equivalent to the versa- tile micromachining approaches used for MEMS fabrication are not available for FE structures to be used in NEMS devices. The currently available processing nanofabrication methods mostly leverage bulk crystallization techniques at temperatures incompatible with complementary metal–oxide–semiconductor (CMOS) processing or lack the registry and alignment required for processing of full devices. Top-down approaches, such as focused ion beam milling, can degrade material properties by creating amorphous surface layers. [2,3] Furthermore, the intrinsic size effects of ferroelectrics [4] become coupled with such extrinsic processing size effects when the surface-to- volume ratio becomes sufficiently high. Similarly, bottom-up approaches have been mostly limited to the creation of arrayed dots and tubes or pillars through the use of ordered-pore structures either as lift-off masks or as infiltration templates, respectively. [5–7] Although nanoimprint can help with the spa- tial registration and shaping of the nano-objects, approaches relying upon ordered-pore templates yield structures of lim- ited geometric variety (i.e., dots or vertically-aligned pillars or tubes). Other methods, such as dip-pen nanolithography [8] and hydrothermal deposition, [9] are strongly coupled to the use of epitaxial substrates, which limits the final device design. A nanomanufacturing method for the creation of arbitrary- shaped planar FE nanostructures without epitaxial-growth requirements is presented here. Ferroelectric lines with widths ≥30 nm and spheres with diameter ≥10 nm and densities up to 213 Gb in −2 are directly fabricated on either plain or plati- nized substrates, ranging from plastic (Kapton) to silicon and soda-lime glass. This process consists of three steps, as illus- trated in Figure 1a: i) deposition of a sol-gel precursor film of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) and PbTiO 3 (PTO) on any substrate capable of withstanding processing temperature of ≈250 °C for one minute (as in step ii); ii) bulk heating of the substrate at 250–300 °C for one minute to remove most of the organics; and iii) local crystallization of the precursor film by thermochemical nanolithography (TCNL), [10–12] where a resistively heated atomic force microscope (AFM) tip [13] is brought in contact (tempera- ture, T contact ≥ 550 °C) with the precursor to form a crystalline FE nanostructure. High-density nanostructure arrays and arbitrary-shaped nanostructures were fabricated. In Figure 1b, the PZT line array, with centers ≈50 nm apart, was fabricated by TCNL using a cantilever heater temperature of ≈1360 °C, which corresponds to a tip–sample contact temperature of ≈608 °C. The line den- sity of the array is ≈0.51 Mb in −1 (corresponding to a 2D density of 258 Gb in −2 ) and it may be further increased by optimizing the TCNL conditions (Figure 1b inset ≈1.02 Mb in −1 ). [14] Lines with average grain size of ≈25 nm, as well as larger grains from a wider line obtained via increased tip–sample contact temperature, are shown in Figure 1b (inset). Additionally, pro- truding (as opposed to “indented”) nanospheres at the den- sity of ≈213 Gb in −2 are presented in Figure 1c. To underscore the versatility of the technique, other structures were created, including the arbitrarily designed shapes or registered nano- spheres as shown in Figure 1d,e. The protruding nanospheres DOI: 10.1002/adma.201101991 Dr. S. Kim, Prof. E. Riedo School of Physics Georgia Institute of Technology Atlanta, GA 30332, USA E-mail: suenne.kim@physics.gatech.edu Y. Bastani, Prof. N. Bassiri-Gharb G. W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta, GA 30332, USA E-mail: nazanin.bassirigharb@me.gatech.edu Dr. H. Lu, Prof. A. Gruverman Department of Physics and Astronomy University of Nebraska-Lincoln Lincoln, NE 68588, USA Prof. W. P. King Department of Mechanical Science and Engineering University of Illinois Urbana-Champaign Urbana, IL 61801, USA Prof. S. Marder, Prof. K. H. Sandhage School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta, GA 30332, USA Prof. S. Marder, Prof. K. H. Sandhage School of Materials Science and Engineering Georgia Institute of Technology Atlanta, GA 30332, USA