Abstract
The nanoscale control afforded by scanning probe microscopes has prompted the development of a wide variety of scanning-probe-based patterning methods. Some of these methods have demonstrated a high degree of robustness and patterning capabilities that are unmatched by other lithographic techniques. However, the limited throughput of scanning probe lithography has prevented its exploitation in technological applications. Here, we review the fundamentals of scanning probe lithography and its use in materials science and nanotechnology. We focus on robust methods, such as those based on thermal effects, chemical reactions and voltage-induced processes, that demonstrate a potential for applications.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 12 print issues and online access
$259.00 per year
only $21.58 per issue
Buy this article
- Purchase on SpringerLink
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Saavedra, H. M. et al. Hybrid strategies in nanolithography. Rep. Prog. Phys. 73, 036501 (2010).
Acikoz, C., Hempenius, M. A., Huskens, J. & Vancso, G. J. Polymers in conventional and alternative lithography for the fabrication of nanosctructures. Eur. Poly. J. 47, 2033–2052 (2011).
Lipson, A. L. & Hersam, M. C. Conductive scanning probe characterization and nanopatterning of electronic and energy materials. J. Phys. Chem. C 117, 7953–7963 (2013).
Pires, D. et al. Nanoscale three-dimensional patterning of molecular resists by scanning probes. Science 328, 732–735 (2010). First implementation of precise three-dimensional relief patterning using thermal scanning probe lithography.
Fuechsle, M. et al. A single-atom transistor. Nature Nanotech. 7, 242–246 (2012).
Martinez, R. V. et al. Large-scale nanopatterning of single proteins used as carriers of magnetic nanoparticles. Adv. Mater. 22, 588–591 (2010).
International Technology Roadmap for Semiconductors 2013 Edition, Lithography Summary; http://www.itrs.net/Links/2013ITRS/2013Chapters/2013Litho_Summary.pdf (2013).
Tennant, D. M. in Nanotechnology (ed. Timp, G.) Ch. 4, 161–205 (Springer, 1999).
Van Oven, J., Berwald, F., Berggren, K., Kruit, P. & Hagen, C. Electron-beam-induced deposition of 3-nm-half-pitch patterns on bulk Si. J. Vac. Sci. Technol. B 29, 06F305 (2011).
de Boer, G. et al. MAPPER: progress toward a high-volume manufacturing system. Proc. SPIE 8680, 86800O (2013).
Gubiotti, T. et al. Reflective electron beam lithography: lithography results using CMOS controlled digital pattern generator chip. Proc. SPIE 8680, 86800H (2013).
van der Drift, E. & Maas, D. J. in Nanotechnology (eds Stepanova, M. & Dew, S.) Ch. 4, 93–116 (Springer, 2012).
Gonzalez, C. M. et al. Focused helium and neon ion beam induced etching for advanced extreme ultraviolet lithography mask repair. J. Vac. Sci. Technol. B 32, 021602 (2014).
Lin, Y. C. et al. Graphene annealing: how clean can it be? Nano Lett. 12, 414–419 (2012).
Martinez, R. V., Martinez, J. & Garcia, R. Silicon nanowire circuits fabricated by AFM oxidation nanolithography. Nanotechnology 21, 245301 (2010).
Weng, L., Zhang, L., Chen, Y. P. & Rokhinson, L. P. Atomic force microscope local oxidation nanolithography of graphene. Appl. Phys. Lett. 93, 093107 (2008).
Kim, S. et al. Direct fabrication of arbitrary-shaped ferroelectric nanostructures on plastic, glass, and silicon substrates. Adv. Mater. 23, 3786–3790 (2011).
Wang, D. et al. Direct writing and characterization of poly(p-phenylene vinylene) nanostructures. Appl. Phys. Lett. 95, 233108 (2009).
Fenwick, O. et al. Thermochemical nanopatterning of organic semiconductors. Nature Nanotech. 4, 664–668 (2009).
Carroll, K. M. et al. Fabricating nanoscale gradients with thermochemical nanolithography. Langmuir 29, 8675–8682 (2013).
Felts, J. R., Onses, M. S., Rogers, J. A. & King, W. P. Nanometer scale alignment of block-copolymer domains by means of a scanning probe tip. Adv. Mater. 26, 2999–3002 (2014).
Carroll, K. M. et al. Parallelization of thermochemical nanolithography. Nanoscale 6, 1299–1304 (2014).
Mamin, H. & Rugar, D. Thermomechanical writing with an atomic force microscope tip. Appl. Phys. Lett. 61, 1003–1005 (1992).
King, W. P. et al. Heated atomic force microscope cantilevers and their applications. Annu. Rev. Heat Transfer 16, 287–326 (2013). Review on scanning probe microscopy and lithography using heatable tips.
Szoszkiewicz, R. et al. High-speed, sub-15 nm feature size thermochemical nanolithography. Nano Lett. 7, 1064–1069 (2007). Example of the capabilities of thermochemical scanning probe lithography for high resolution and fast nanopatterning.
Gotsmann, B., Duerig, U., Frommer, J. & Hawker, C. J. Exploiting chemical switching in a Diels-Alder polymer for nanoscale probe lithography and data storage. Adv. Funct. Mater. 16, 1499–1505 (2006).
Cheong, L. L. et al. Thermal probe mask-less lithography for 27.5 nm half-pitch Si technology. Nano Lett. 13, 4485–4491 (2013).
Knoll, A. W. et al. Probe-based 3-D nanolithography using self-amplified depolymerization polymers. Adv. Mater. 22, 3361–3365 (2010).
Paul, P., Knoll, A., Holzner, F., Despont, M. & Duerig, U. Rapid turnaround scanning probe nanolithography. Nanotechnology 22, 275306 (2011).
Paul, P., Knoll, A., Holzner, F. & Duerig, U. Field stitching in thermal probe lithography by means of surface roughness correlation. Nanotechnology 23, 385307 (2012).
Shaw, J. E., Stavrinou, P. N. & Anthopoulos, T. D. On-demand patterning of nanostructured pentacene transistors by scanning thermal lithography. Adv. Mater. 25, 552–558 (2013). On-demand patterning of field-effect transistors from a pentacene precursor by thermal scanning probe lithography.
Wei, Z. et al. Nanoscale tunable reduction of graphene oxide for graphene electronics. Science 328, 1373–1376 (2010).
Lee, W.-K. et al. Nanoscale reduction of graphene fluoride via thermochemical nanolithography. ACS Nano 7, 6219–6224 (2013).
Duvigneau, J., Schoenherr, H. & Vancso, G. J. Atomic force microscopy based thermal lithography of poly(tert-butyl acrylate) block copolymer films for bioconjugation. Langmuir 24, 10825–10832 (2008).
Wang, D. et al. Thermochemical nanolithography of multifunctional nanotemplates for assembling nano-objects. Adv. Funct. Mater. 19, 3696–3702 (2009).
Holzner, F. et al. Directed placement of gold nanorods using a removable template for guided assembly. Nano Lett. 11, 3957–3962 (2011).
Holzner, F. et al. High density multi-level recording for archival data preservation. Appl. Phys. Lett. 99, 023110 (2011).
Torrey, J. et al. Scanning probe direct-write of germanium nanostructures. Adv. Mater. 22, 4639–4642 (2010).
Garcia, R. et al. Nanopatterning of carbonaceous structures by field-induced carbon dioxide splitting with a force microscope. Appl. Phys. Lett. 96, 143110 (2010).
Suez, I. et al. High-field scanning probe lithography in hexadecane: Transitioning from field induced oxidation to solvent decomposition through surface modification. Adv. Mater. 19, 3570–3573 (2007).
Dagata, J. A. et al. Modification of hydrogen-passivated silicon by a scanning tunneling microscope operating in air. Appl. Phys. Lett. 56, 2001–2003 (1990).
Garcia, R., Martinez, R. V. & Martinez, J. Nanochemistry and scanning probe nanolithographies. Chem. Soc. Rev. 35, 29–38 (2006).
Yan, N. et al. Water-mediated electrochemical nano-writing on thin ceria films. Nanotechnology 25, 075701 (2014).
Li, Y., Maynor, B. W. & Liu, J. Electrochemical AFM 'dip-pen' nanolithography. J. Am. Chem. Soc. 123, 2105–2106 (2001).
Arruda, T. M. et al. Toward quantitative electrochemical measurements on the nanoscale by scanning probe microscopy: Environmental and current spreading effects. ACS Nano 7, 8175–8182 (2013).
Wei, Y. M. et al. The creation of nanostructures on an Au(111) electrode by tip-induced iron deposition from an ionic liquid. Small 4, 1355–1358 (2008).
Obermair, C., Kress, M., Wagner, A. & Schimmel, T. Reversible mechano-electrochemical writing of metallic nanostructures with the tip of an atomic force microscope. Beilstein J. Nanotech. 3, 824–830 (2012).
Zhang, K. et al. Direct writing of electronic devices on graphene oxide by catalytic scanning probe lithography. Nature Commun. 3, 1194 (2012).
Liu, J.-F. & Miller, G. P. Field-assisted nanopatterning of metals, metal oxides and metal salts. Nanotechnology 20, 055303 (2009).
Ferris, R. et al. Field-induced nanolithography for patterning of non-fouling polymer brush surfaces. Small 7, 3032–3037 (2011).
Kaestner, M., Hofer, M. & Rangelow, I. W. Nanolithography by scanning probes on calixarene molecular glass resist using mix-and-match lithography. J. Micro/Nanolith. MEMS MOEMS 12, 031111 (2013).
Lyuksyutov, S. F. et al. Electrostatic nanolithography in polymers using atomic force microscopy. Nature Mater. 2, 468–472 (2003).
Lyding, J. W., Shen, T. C., Hubacek, J. S., Tucker, J. R. & Abeln, G. C. Nanoscale patterning and oxidation of H-passivated Si(100)-2×1 surfaces with an ultrahigh-vacuum scanning tunneling microscope. Appl. Phys. Lett. 64, 2010–2012 (1994).
Blanco, E. M., Nesbitt, S. A., Horton, M. A. & Mesquida, P. A multiprotein microarray on silicon dioxide fabricated by using electric-droplet lithography. Adv. Mater. 19, 2469–2473 (2007).
Cho, Y., Hashimoto, S., Odagawa, N., Tanaka, K. & Hiranaga, Y. Nanodomain manipulation for ultrahigh density ferroelectric data storage. Nanotechnology 17, S137–S141 (2006).
Tayebi, N. et al. Tuning the built-in electric field in ferroelectric Pb(Zr0.2Ti0.8)O3 films for long-term stability of single-digit nanometer inverted domains. Nano Lett. 12, 5455–5463 (2012).
Weber, B. et al. Ohm's law survives to the atomic scale. Science 335, 64–67 (2012).
Weber, B., Mahapatra, S., Watson, T. & Simmons, M. Y. Engineering independent electrostatic control of atomic-scale (∼4 nm) silicon double quantum dots. Nano Lett. 12, 4001–4006 (2012).
Tayebi, N. et al. An ultraclean tip-wear reduction scheme for ultrahigh density scanning probe-based data storage. ACS Nano 4, 5713–5720 (2010).
Forrester, M. et al. Charge-based scanning probe readback of nanometer-scale ferroelectric domain patterns at megahertz rates. Nanotechnology 20, 225501 (2009).
Martinez, R. V., Losilla, N. S., Martinez, J. & Garcia, R. Patterning polymeric structures with 2 nm resolution at 3 nm half pitch in ambient conditions. Nano Lett. 7, 1846–1850 (2007). This contribution reports the smallest periodic pattern fabricated on silicon at atmospheric pressure and room temperature.
Vasko, S. E. et al. Serial and parallel Si, Ge, and SiGe direct-write with scanning probes and conducting stamps. Nano Lett. 11, 2386–2389 (2011).
Lyo, I. W. & Avouris, P. Field-induced nanometer-scale to atomic-scale manipulation of silicon surfaces with the STM. Science 253, 173–176 (1991).
Eigler, D. M. & Schweizer, E. K. Positioning single atoms with a scanning tunneling microscope. Nature 344, 524–526 (1990).
Custance, O., Perez, R. & Morita, S. Atomic force microscopy as a tool for atom manipulation. Nature Nanotech. 4, 803–810 (2009). Review on the use of the force microscope for atomic-scale manipulation.
Minne, S. C. et al. Centimeter scale atomic force microscope imaging and lithography. Appl. Phys. Lett. 73, 1742–1744 (1998).
Lorenzoni, M. & Torre, B. Scanning probe oxidation of SiC, fabrication and kinetics considerations. Appl. Phys. Lett. 103, 163109 (2013).
Kim, H. et al. Effects of ion beam irradiated Si on atomic force microscopy local oxidation. Chem. Phys. Lett. 566, 44–49 (2013).
Zeira, A. et al. A bipolar electrochemical approach to constructive lithography: metal/monolayer patterns via consecutive site-defined oxidation and reduction. Langmuir 27, 8562–8575 (2011).
Fabre, B. & Herrier, C. Automated sub-100 nm local anodic oxidation-directed nanopatterning of organic monolayer-modified silicon surfaces. RSC Adv. 2, 168–175 (2012).
Meroni, D., Ardizzone, S., Schubert, U. S. & Hoeppener, S. Probe-based electro-oxidative lithography of OTS SAMs deposited onto transparent ITO substrates. Adv. Funct. Mater. 22, 4376–4382 (2012).
Martin-Olmos, C. et al. Conductivity of SU-8 thin films through atomic force microscopy nano-patterning. Adv. Funct. Mater. 22, 1482–1488 (2012).
Martinez, R. V. et al. Nanoscale deposition of single-molecule magnets onto SiO2 patterns. Adv. Mater. 19, 291–295 (2007).
Berson, J., Zeira, A., Maoz, R. & Sagiv, J. Parallel- and serial-contact electrochemical metallization of monolayer nanopatterns: A versatile synthetic tool en route to bottom-up assembly of electric nanocircuits. Beilstein J. Nanotech. 3, 134–143 (2012). Comprehensive study of the use of oxidation scanning probe lithography to pattern organic monolayers and their use as templates for the deposition of metallic nanoparticles.
Coronado, E. et al. Nanopatterning of anionic nanoparticles based on magnetic prussian-blue analogues. Adv. Funct. Mater. 22, 3625–3633 (2012).
Khatri, O. P., Han, J., Ichiii, T., Murase, K. & Sugimura, H. J. Self-assembly guided one-dimensional arrangement of gold nanoparticles: A facile approach. J. Phys. Chem. C 112, 16182–16185 (2008).
Oria, L., Ruiz de Luzuriaga, A., Alduncín, J. A. & Perez-Murano, F. Polystyrene as a brush layer for directed self-assembly of block co-polymers. Microelec. Eng. 110, 234–240 (2013).
Benetti, E. M., Chung, H. J. & Vancso, G. J. pH responsive polymeric brush nanostructures: Preparation and characterization by scanning probe oxidation and surface initiated polymerization. Macromol. Rapid Commun. 30, 411–417 (2009).
Druzhinina, T. S., Hoeppener, C., Hoeppener, S. & Schubert, U. S. Hierarchical, guided self-assembly of preselected carbon nanotubes for the controlled fabrication of CNT structures by electrooxidative nanolithography. Langmuir 29, 7515–7520 (2013).
Martin-Sanchez, J., Alonso-Gonzalez, P., Herranz, J., Gonzalez, Y. & Gonzalez, L. Site-controlled lateral arrangements of InAs quantum dots grown on GaAs(001) patterned substrates by atomic force microscopy local oxidation nanolithography. Nanotechnology 20, 125302 (2009).
Delacour, C., Pannetier, B., Villegier, J. C. & Bouchiat, V. Quantum and thermal phase slips in superconducting niobium nitride (NbN) ultrathin crystalline nanowire: Application to single photon detection. Nano Lett. 12, 3501–3506 (2012).
Yokoo, A., Tanabe, T., Kuramochi, E. & Notomi, M. Ultrahigh-Q nanocavities written with a nanoprobe. Nano Lett. 11, 3634–3642 (2011).
Komijani, Y. et al. Origins of conductance anomalies in a p-type GaAS quantum point contact. Phys. Rev. B 87, 245406 (2013).
Fuhrer, A. S. et al. Energy spectra of quantum rings. Nature 413, 822–825 (2001).
Ubbelohde, N., Fricke, C., Hohls, F. & Haug, R. J. Spin-dependent shot noise enhancement in a quantum dot. Phys. Rev. B 88, 041304 (2013).
Tsai, J. T. H., Hsu, C. H., Hsu, C. Y. & Yang, C. S. Rapid synthesis of gallium oxide resistive random access memory by atomic force microscopy local anodic oxidation. Electron. Lett. 49, 554–555 (2013).
Schmidt, H., Rode, J. C., Belke, C., Smirnov, D. & Haug, R. J. Mixing of edge states at a bipolar graphene junction. Phys. Rev. B 88, 075418 (2013).
Kurra, N., Reifenberger, R. G. & Kulkarni, G. U. Nanocarbon-scanning probe microscopy synergy: Fundamental aspects to nanoscale devices. ACS Appl. Mater. Interf. 6, 6147–6163 (2014).
Byun, I. S. et al. Nanoscale lithography on monolayer graphene using hydrogenation and oxidation. ACS Nano 5, 6417–6424 (2011).
Puddy, R. K., Chua, C. J. & Buitelaar, M. R. Transport spectroscopy of a graphene quantum dot fabricated by atomic force microscope nanolithography. Appl. Phys. Lett. 103, 183117 (2013).
Neubek, S. et al. From one electron to one hole: Quasiparticle counting in graphene quantum dots determined by electrochemical and plasma etching. Small 6, 1469–1473 (2010).
Masubuchi, S., Arai, M. & Machida, T. Atomic force microscopy based tunable local anodic oxidation of graphene. Nano Lett. 11, 4542–4546 (2011).
Matsumoto, K., Gotoh, Y., Maeda, T., Dagata, J. A. & Harris, J. S. Room-temperature single-electron memory made by pulse-mode atomic force microscopy nano oxidation process on atomically flat α-alumina substrate. Appl. Phys. Lett. 76, 239–241 (2000).
Snow, E. S. & Campbell, P. M. AFM fabrication of sub-10 nanometer metal-oxide devices with in situ control of electrical properties. Science 270, 1639–1641 (1995). One of the earliest applications of oxidation scanning probe lithography to fabricate nanoscale transistors.
Larki, F. et al. Pinch-off mechanism in double-lateral-gate junctionless transistors fabricated by scanning probe microscope based lithography. Beilstein J. Nanotech. 3, 817–823 (2012).
Cavallini, M. et al. Additive nanoscale embedding of functional nanoparticles on silicon surface. Nanoscale 2, 2069–2072 (2010).
Cramer, T., Zerbetto, F. & Garcia, R. Molecular mechanism of water bridge buildup: Field-induced formation of nanoscale menisci. Langmuir 24, 6116–6120 (2008).
Skinner, L. B. et al. Structure of the floating water bridge and water in an electric field. Proc. Natl Acad. Sci. USA 109, 16463–16468 (2012).
Calleja, M., Tello, M. & Garcia, R. Size determination of field-induced water menisci in noncontact atomic force microscopy. J. Appl. Phys. 92, 5539–5542 (2002).
Kinser, C. R., Schmitz, M. J. & Hersam, M. C. Kinetics and mechanism of atomic force microscope local oxidation on hydrogen-passivated silicon in inert organic solvents. Adv. Mater. 18, 1377–1380 (2006).
Maoz, R., Cohen, S. R. & Sagiv, J. Nanoelectrochemical patterning of monolayer surfaces: Toward spatially defined self-assembly of nanostructures. Adv. Mater. 11, 55–61 (1999).
Ryu, Y. K., Chiesa, M. & Garcia, R. Electrical characteristics of silicon nanowire transistors fabricated by scanning probe and electron beam lithographies. Nanotechnology 24, 315205 (2013).
Chiesa, M. et al. Detection of the early stage of recombinational DNA repair by silicon nanowire transistors. Nano Lett. 12, 1275–1281 (2012).
Tseng, A. A. Removing material using atomic force microscopy with single- and multiple-tip sources. Small 7, 3409–3427 (2011).
Meister, A. et al. FluidFM: Combining atomic force microscopy and nanofluidics in a universal liquid delivery system for single cell applications and beyond. Nano Lett. 9, 2501–2507 (2009).
Salaita, K., Wang, Y. & Mirkin, C. A. Applications of dip-pen nanolithography. Nature Nanotech. 2, 145–155 (2007).
Chen, H.-A., Lin, H.-Y. & Lin, H.-N. Localized surface plasmon resonance in lithographically fabricated single gold nanowires. J. Phys. Chem. C 114, 10359–10364 (2010).
Shim, W. et al. Plow and ridge nanofabrication. Small 9, 3058–3062 (2013).
Ngunjiri, J. & Garno, J. C. AFM-based lithography for nanoscale protein assays. Anal. Chem. 80, 1361–1369 (2008).
Taha, H. et al. Protein printing with an atomic force sensing nanofountainpen. Appl. Phys. Lett. 83, 1041–1043 (2003).
Bellido, E., de Miguel, R., Ruiz-Molina, D., Lostao, A. & Maspoch, D. Controlling the number of proteins with dip-pen nanolithography. Adv. Mater. 22, 352–355 (2010).
Lee, W.-K., Whitman, L. J., Lee, J., King, W. P. & Sheehan, P. E. The nanopatterning of a stimulus-responsive polymer by thermal dip-pen nanolithography. Soft Matter 4, 1844–1847 (2008).
Lee, W.-K. et al. Chemically isolated graphene nanoribbons reversibly formed in fluorographene using polymer nanowire masks. Nano Lett. 11, 5461–5464 (2011).
Ando, T., Uchihashi, T. & Kodera, N. High-speed AFM and applications to biomolecular systems. Annu. Rev. Biophys. 42, 393–414 (2013).
Mirkin, C. A. The power of the pen: Development of massively parallel dip-pen nanolithography. ACS Nano 1, 79–83 (2007).
Eichelsdoerfer, D. J. Large-area molecular patterning with polymer pen lithography. Nature Protoc. 8, 2548–2560 (2013).
Liao, X. et al. Desktop nanofabrication with massively multiplexed beam pen lithography. Nature Commun. 4, 2103 (2013).
Koelmans, W. et al. Parallel optical readout of cantilever arrays in dynamic mode. Nanotechnology 21, 395503 (2010).
Michels, T. & Rangelow, I. W. Review on scanning probe micromachining and its applications within nanoscience. Microelectron. Eng. http://dx.doi.org/10.1016/j.mee.2014.02.011 (2014).
Pantazi, A. et al. Probe-based ultrahigh-density storage technology. IBM J. Res. Dev. 52, 493–511 (2010).
Cavallini, M. et al. Regenerable resistive switching in silicon oxide based nanojunctions. Adv. Mater. 24, 1197–1201 (2012).
Zeira, A., Chowdhury, D., Maoz, R. & Sagiv, J. Contact electrochemical replication of hydrophilic-hydrophobic monolayer patters. ACS Nano 2, 2554–2568 (2008).
Sugimoto, Y. et al. Chemical identification of individual surface atoms by atomic force microscopy. Nature 446, 64–67 (2007).
Herruzo, E. T., Perrino, A. P. & Garcia, R. Fast nanomechanical spectroscopy of soft matter. Nature Commun. 5, 3126 (2014).
Rice, R. H., Mokarian-Tabari, P., King, W. P. & Szoszkiewicz, R. Local thermomechanical analysis of a microphase-separated thin lamellar PS-b-PEO film. Langmuir 28, 13503–13511 (2012).
Holzner, F. et al. Thermal probe nanolithography: In-situ inspection, high-speed, high-resolution, 3D. Proc. SPIE 8886, 888605 (2013).
Acknowledgements
Financial support from the European Research Council AdG no. 340177 (R.G.) and StG no. 307079 (A.W.K.), the European Commission FP7-ICT-2011 no. 318804 (R.G. and A.W.K.), the Swiss National Science Foundation SNSF no. 200020-144464 (A.W.K.), the Ministerio de Economía y Competitividad MAT2013-44858-R (R.G.), the National Science Foundation CMMI-1100290 (E.R.), the MRSEC program DMR-0820382 (E.R.) and the Office of Basic Energy Sciences of the Department of Energy DE-SC0002245 (E.R.) are acknowledged.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing financial interests.
Rights and permissions
About this article
Cite this article
Garcia, R., Knoll, A. & Riedo, E. Advanced scanning probe lithography. Nature Nanotech 9, 577–587 (2014). https://doi.org/10.1038/nnano.2014.157
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/nnano.2014.157