Skip to main content Accessibility help
×
Home

Modern Focused-Ion-Beam-Based Site-Specific Specimen Preparation for Atom Probe Tomography

  • Ty J. Prosa (a1) and David J. Larson (a1)

Abstract

Approximately 30 years after the first use of focused ion beam (FIB) instruments to prepare atom probe tomography specimens, this technique has grown to be used by hundreds of researchers around the world. This past decade has seen tremendous advances in atom probe applications, enabled by the continued development of FIB-based specimen preparation methodologies. In this work, we provide a short review of the origin of the FIB method and the standard methods used today for lift-out and sharpening, using the annular milling method as applied to atom probe tomography specimens. Key steps for enabling correlative analysis with transmission electron-beam backscatter diffraction, transmission electron microscopy, and atom probe tomography are presented, and strategies for preparing specimens for modern microelectronic device structures are reviewed and discussed in detail. Examples are used for discussion of the steps for each of these methods. We conclude with examples of the challenges presented by complex topologies such as nanowires, nanoparticles, and organic materials.

Copyright

Corresponding author

* Corresponding author. ty.prosa@ametek.com

References

Hide All
Agrawal, R., Bernal, R.A., Isheim, D. & Espinosa, H.D. (2011). Characterizing atomic composition and dopant distribution in wide band gap semiconductor nanowires using laser-assisted atom probe tomography. J Phys Chem C 115, 1768817694.
Alexander, K.B., Angelini, P. & Miller, M.K. (1989). Precision ion milling of field-ion specimens. J Phys (Paris), Colloq 50, 549554.
Arslan, I., Marquis, E.A., Homer, M., Hekmaty, M.A. & Bartelt, N.C. (2008). Towards better 3-D reconstructions by combining electron tomography and atom-probe tomography. Ultramicroscopy 108, 15791585.
Babinsky, K., De Kloe, R., Clemens, H. & Primig, S. (2014). A novel approach for site-specific atom probe specimen preparation by focused ion beam and transmission electron backscatter diffraction. Ultramicroscopy 144, 918.
Babinsky, K., Knabl, W., Lorich, A., De Kloe, R., Clemens, H. & Primig, S. (2015). Grain boundary study of technically pure molybdenum by combining APT and TKD. Ultramicroscopy 159, (Pt 2), 445451.
Birdseye, P.J., Smith, D.A. & Smith, G.D.W. (1974). Analogue investigations of electric field distribution and ion trajectories in the field ion microscope. J Phys D 7, 16421651.
Blumtritt, H., Isheim, D., Senz, S., Seidman, D.N. & Moutanabbir, O. (2014). Preparation of nanowire specimens for laser-assisted atom probe tomography. Nanotechnology 25, 435704.
Bran, J., Jean, M., Lardé, R., Sauvage, X., Breton, J.-M.L. & Pautrat, A. (2013). Elaboration and characterization of Cu/Co multilayered nanowires. J Korean Phys Soc 62, 17441747.
Chen, Y., Rice, K.P., Prosa, T.J., Marquis, E.A. & Reed, R.C. (2015). Integrated APT/t-EBSD for grain boundary analysis of thermally grown oxide on a Ni-based superalloy. Microsc Microanal 21, 687688.
Chen, Y., Rice, K.R. & Prosa, T.J. (2016). Site-specific sample preparation using correlative microscopy: APT and tEBSD. Microsc Anal Suppl May/June (S4).
Cojocaru-Mirédin, O., Pyuck-Pa, C., Abou-Ras, D., Schmidt, S.S., Caballero, R. & Raabe, D. (2011). Characterization of grain boundaries in Cu(In,Ga)Se films using atom-probe tomography. IEEE J Photovolt 1, 207212.
Diercks, D.R., Gorman, B.P. & Mulders, J.J.L. (in submission). Electron beam induced deposition for atom probe tomography specimen capping layers. Microsc Microanal. doi:10.1017/S1431927616011740.
Diercks, D.R., Tong, J., Zhu, H., Kee, R., Baure, G., Nino, J.C., O’Hayre, R. & Gorman, B.P. (2016). Three-dimensional quantification of composition and electrostatic potential at individual grain boundaries in doped ceria. J Mater Chem A 4, 51675175.
Eaton, H.C. & Bayuzick, R.J. (1978). Field-induced stresses in field emitters. Surf Sci 70, 408426.
Eichfeld, C.M., Gerstl, S.S.A., Prosa, T., Ke, Y., Redwing, J.M. & Mohney, S.E. (2012). Local electrode atom probe analysis of silicon nanowires grown with an aluminum catalyst. Nanotechnology 23, 215205.
El Kousseifi, M., Panciera, F., Hoummada, K., Descoins, M., Baron, T. & Mangelinck, D. (2014). Ni silicide nanowires analysis by atom probe tomography. Microelectron Eng 120, 4751.
Estivill, R., Audoit, G., Barnes, J.-P., Grenier, A. & Blavette, D. (2016). Preparation and analysis of atom probe tips by xenon focused ion beam milling. Microsc Microanal 22, 576582.
Felfer, P., Alam, T., Ringer, S.P. & Cairney, J.M. (2012). A reproducible method for damage-free site-specific preparation of atom probe tips from interfaces. Microsc Res Tech 75, 484491.
Felfer, P., Benndorf, P., Masters, A., Maschmeyer, T. & Cairney, J.M. (2014). Revealing the distribution of the atoms within individual bimetallic catalyst nanoparticles. Angew Chem Int Ed Engl 53, 1119011193.
Felfer, P. & Cairney, J. (2011a). New equipment for correlative FIB/TEM/atom probe and site-specific preparation using STEM live imaging. Microsc Microanal 17(S2), 756757.
Felfer, P., Li, T., Eder, K., Galinski, H., Magyar, A.P., Bell, D.C., Smith, G.D.W., Kruse, N., Ringer, S.P. & Cairney, J.M. (2015). New approaches to nanoparticle sample fabrication for atom probe tomography. Ultramicroscopy 159(Pt 2), 413419.
Felfer, P., Ringer, S.P. & Cairney, J.M. (2011b). Shaping the lens of the atom probe: Fabrication of site specific, oriented specimens and application to grain boundary analysis. Ultramicroscopy 111, 435439.
Folcke, E., Larde, R., Le Breton, J.M., Gruber, M., Vurpillot, F., Shield, J.E., Rui, X. & Patterson, M.M. (2012). Laser-assisted atom probe tomography investigation of magnetic FePt nanoclusters: First experiments. J Alloy Compd 517, 4044.
Gault, B., Moody, M. P., Cairney, J.M. & Ringer, S.P. (2012). Atom Probe Microscopy. New York: Springer.
Giannuzzi, L.A., Drown, J.I., Brown, S.R., Irwin, R.B. & Stevie, F.A. (1997). Focused ion beam milling and micromanipulation lift-out for site specific cross-section TEM specimen preparation. Mater Res Soc Symp Proc 480, 1927.
Gilbert, M., Vandervorst, W., Koelling, S. & Kambham, A.K. (2011). Atom probe analysis of a 3D finFET with high-k metal gate. Ultramicroscopy 111, 530534.
Gordon, L.M., Cohen, M.J. & Joester, D. (2013). Towards atom probe tomography of hybrid organic-inorganic nanoparticles. Microsc Microanal 19(S2), 952953.
Gorman, B.P., Diercks, D., Salmon, N., Stach, E., Amador, G. & Hartfield, C. (2008). Hardware and techniques for cross-correlative TEM and atom probe analysis. Microsc Today 16, 4247.
Greene, M.E., Kelly, T.F., Larson, D.J. & Prosa, T.J. (2012). Focused ion beam fabrication of solidified ferritin into nanoscale volumes for compositional analysis using atom probe tomography. J Microsc 247, 288299.
Grenier, A., Duguay, S., Barnes, J.P., Serra, R., Rolland, N., Audoit, G., Morin, P., Gouraud, P., Cooper, D., Blavette, D. & Vurpillot, F. (2015). Three dimensional imaging and analysis of a single nano-device at the ultimate scale using correlative microscopy techniques. Appl Phys Lett 106, 213102.
Haley, D., Petersen, T., Ringer, S.P. & Smith, G.D.W. (2011). Atom probe trajectory mapping using experimental tip shape measurements. J Microsc 244, 170180.
Hartshorne, M.I., Isheim, D., Seidman, D.N. & Taheri, M.L. (2014). Specimen preparation for correlating transmission electron microscopy and atom probe tomography of mesoscale features. Ultramicroscopy 147, 2532.
Heck, P.R., Pellin, M.J., Davis, A.M., Martin, I., Renaud, L., Benbalagh, R., Isheim, D., Seidman, D.N., Hiller, J., Stephan, T., Lewis, R.S., Savina, M.R., Mane, A., Elam, J., Stadermann, F.J., Zhao, X., Daulton, T.L. & Amara, S. (2010). Atom-probe tomographic analyses of presolar silicon carbide grains and meteoric nanodiamonds – first results on silicon carbide. In 41st Lunar and Planetary Science Conference, The Woodlands, Texas. Submission 2112.
Heck, P.R., Stadermann, F.J., Isheim, D., Auciello, O., Daulton, T.L., Davis, A.M., Elam, J.W., Floss, C., Hiller, J., Larson, D.J., Lewis, J.B., Mane, A., Pellin, M.J., Savina, M.R., Seidman, D. N. & Stephan, T. (2014). Atom-probe analyses of nanodiamonds from Allende. Meteorit Planet Sci 49, 453467.
Henjered, A. & Norden, H. (1983). A controlled specimen preparation technique for interface studies with atom-probe field-ion microscopy. J Phys E 16, 617619.
Herbig, M., Choi, P. & Raabe, D. (2015). Combining structural and chemical information at the nanometer scale by correlative transmission electron microscopy and atom probe tomography. Ultramicroscopy 153, 3239.
Herbig, M., Raabe, D., Li, Y.J., Choi, P, Zaefferer, S. & Goto, S. (2014). Atomic-scale quantification of grain boundary segregation in nanocrystalline material. Phys Rev Lett 112, 126103.
Isheim, D., Kaszpurenko, J., Yu, D., Mao, Z., Seidman, D.N. & Arslan, I. (2012). 3-D atomic-scale mapping of manganese dopants in lead sulfide nanowires. J Phys Chem C 116, 65956600.
Kambham, A.K., Mody, J., Gilbert, M., Koelling, S. & Vandervorst, W. (2011). Atom-probe for FinFET dopant characterization. Ultramicroscopy 111, 535539.
Keller, R.R. & Geiss, R.H. (2012). Transmission EBSD from 10 nm domains in a scanning electron microscope. J Microsc 245, 245251.
Kubota, M., Takamizawa, H., Shimizu, Y., Nozawa, Y., Ebisawa, N., Toyama, T., Ishida, Y., Yanagiuchi, K., Inoue, K. & Nagai, Y. (2015). Elemental distribution in multilayer systems by laser-assisted atom probe tomography with various analysis directions. Microsc Microanal 21, 13731378.
Larson, D.J., Foord, D.T., Petford-Long, A.K., Anthony, T.C., Rozdilsky, I.M., Cerezo, A. & Smith, G.D.W. (1998b). Focused ion-beam milling for field-ion specimen preparation: preliminary investigations. Ultramicroscopy 75, 147159.
Larson, D.J., Foord, D.T., Petford-Long, A.K., Liew, H., Blamire, M.G., Cerezo, A. & Smith, G.D.W. (1999). Field-ion specimen preparation using focused ion-beam milling. Ultramicroscopy 79, 287293.
Larson, D.J., Gault, B., Geiser, B.P., De Geuser, F. & Vurpillot, F. (2013a). Atom probe tomography spatial reconstruction: Status and directions. Curr Opin Solid State Mater Sci 17, 236247.
Larson, D.J., Giddings, A.D., Wu, Y., Verheijen, M.A., Prosa, T.J., Roozeboom, F., Rice, K.P., Kessels, W.M.M., Geiser, B.P. & Kelly, T.F. (2015). Encapsulation method for atom probe tomography analysis of nanoparticles. Ultramicroscopy 159, 420426.
Larson, D.J., Lawrence, D., Olson, D., Prosa, T.J., Ulfig, R.M., Reinhard, D.A., Clifton, P.C., Kelly, T.F. & Lefebvre, W. (2011a). From the store shelf to device-level atom probe analysis: An exercise in feasibility. In 36th International Symposium for Testing and Failure Analysis, ASM International, San Jose, California, pp. 189–197.
Larson, D.J., Marquis, E.A., Rice, P.M., Prosa, T.J., Geiser, B.P., Yang, S.-H. & Parkin, S.S.P. (2011b). Manganese diffusion in annealed magnetic tunnel junctions with MgO tunnel barriers. Scripta Mater 64, 673676.
Larson, D.J., Miller, M.K., Ulfig, R.M., Matyi, R.J., Camus, P.P. & Kelly, T.F. (1998b). Field ion specimen preparation from near-surface regions. Ultramicroscopy 73, 273278.
Larson, D.J., Prosa, T.J., Bunton, J.H., Olson, D.P., Lawrence, D.F., Oltman, E., Strennen, S.N. & Kelly, T.F. (2013b). Improved mass resolving power and yield in atom probe tomography. Microsc Microanal 19(S2), 994995.
Larson, D.J., Prosa, T.J., Geiser, B.P. & Egelhoff, W.F. Jr. (2011c). Effect of analysis direction on the measurement of interfacial mixing in thin metal layers with atom probe tomography. Ultramicroscopy 111, 506511.
Larson, D.J., Prosa, T.J., Lawrence, D., Geiser, B.P., Jones, C.M. & Kelly, T.F. (2011d). Atom probe tomography for microelectronics. In Handbook of Instrumentation and Techniques for Semiconductor Nanostructure Characterization, vol. 2, Haight, R., Ross, F. & Hannon, J. (Eds.), pp. 407–477. London: World Scientific Publishing.
Larson, D.J., Prosa, T.J., Perea, D.E., Inoue, K. & Mangelinck, D. (2016). Atom probe tomography of nanoscale electronic materials. MRS Bull 41, 3034.
Larson, D.J., Prosa, T.J., Ulfig, R.M., Geiser, B.P. & Kelly, T.F. (2013c). Local Electrode Atom Probe Tomography: A User’s Guide. New York: Springer.
Lawrence, D., Alvis, R. & Olson, D. (2008). Specimen preparation for cross-section atom probe analysis. Microsc Microanal 14(S2), 10041005.
Lawrence, D.F., Olson, D.P., Larson, D.J. & Francois-Saint-Cyr, F. (2015). FIB-SEM sample preparation for atom probe tomography. In FIB SEM User Group Meeting, Laurel, MD.
Lawrence, D.F., Ulfig, R.M., Olson, D.P., Reinhard, D.A., Martin, I., Strennen, S.N. & Clifton, P.H. (2014). Routine device-level atom probe analysis. In Proceedings of the 40th International Symposium for Testing and Failure Analysis, Houston, Texas, 19–22.
Lefebvre, W., Hernandez-Maldonado, D., Moyon, F., Cuvilly, F., Vaudolon, C., Shinde, D. & Vurpillot, F. (2015). HAADF–STEM atom counting in atom probe tomography specimens: Towards quantitative correlative microscopy. Ultramicroscopy 159, 403412.
Martin, A.J., Weng, W., Zhu, Z., Loesing, R., Shaffer, J. & Katnani, A. (2016). Cross-sectional atom probe tomography sample preparation for improved analysis of fins on SOI. Ultramicroscopy 161, 105109.
Melmed, A.J. (1991). The art and science and other aspects of making sharp tips. J Vac Sci Technol B9, 601609.
Melmed, A.J. (1996). Recollections of Erwin Muller’s Laboratory: The development of FIM (1951-1956). Appl Surf Sci 94/95, 1725.
Miller, M.K. & Forbes, R.G. (2014). Atom-Probe Tomography: The Local Electrode Atom Probe, 1st ed. New York: Springer.
Miller, M.K., Russell, K.F. & Thompson, G.B. (2005). Strategies for fabricating atom probe specimens with a dual beam FIB. Ultramicroscopy 102, 287298.
Miller, M.K., Russell, K.F., Thompson, K., Alvis, R. & Larson, D.J. (2007). Review of atom probe FIB-based specimen preparation methods. Microsc Microanal 13, 428436.
Moody, M.P., Vella, A., Gerstl, S.S.A. & Bagot, P.A.J. (2016). Advances in atom probe tomography instrumentation: Implications for materials research. MRS Bull 41, 4045.
Moore, J., Jones, K.S., Kennel, H. & Corcoran, S. (2008). 3-D analysis of semiconductor dopant distributions in a patterned structure using LEAP. Ultramicroscopy 108, 536539.
Nastasi, M., Mayer, J.W. & Hirvonen, J.K. (1996). Ion-Solid Interactions: Fundamentals and Applications. New York: Oxford University Press.
Overwijk, M.H.F., van den Heuvel, F.C. & Bulle-Lieuwma, C.W.T (1993). Novel scheme for the preparation of transmission electron-microscopy specimens with a focused ion-beam. J Vac Sci Technol B 11, 2021.
Padalkar, S., Riley, J.R., Li, Q., Wang, G.T. & Lauhon, L.J. (2014). Lift-out procedures for atom probe tomography targeting nanoscale features in core-shell nanowire heterostructures. Phys Status Solidi C 11, 656661.
Panitz, J.A., McLane, S.B. & Muller, E.W. (1969). Calibration of the atom probe FIM. Rev Sci Instrum 40, 13211324.
Perea, D.E., Liu, J., Bartrand, J., Dicken, Q., Thevuthasan, S.T., Browning, N.D. & Evans, J.E. (2016). Atom probe tomographic mapping directly reveals the atomic distribution of phosphorus in resin embedded ferritin. Sci Rep 6, 22321.
Perea, D.E., Wijaya, E., Lensch-Falk, J.L., Hemesath, E.R. & Lauhon, L.J. (2008). Tomographic analysis of dilute impurities in semiconductor nanostructures. J Solid State Chem 181, 16451652.
Prosa, T.J., Alvis, R., Tsakalakos, L. & Smentkowski, V.S. (2010). Characterization of dilute species within CVD-grown silicon nanowires doped using trimethylboron: Protected lift-out specimen preparation for atom probe tomography. J Microsc 239, 9298.
Prosa, T.J., Clifton, P.H., Zhong, H., Tyagi, A., Shivaraman, R., DenBaars, S.P., Nakamura, S. & Speck, J.S. (2011). Atom probe analysis of interfacial abruptness and clustering within a single In(x)Ga(1-x)N quantum well device on semipolar (10(1)over-bar(1)over-bar) GaN substrate. Appl Phys Lett 98, 191903191905.
Prosa, T.J., Geiser, B.P., Lawrence, D., Olson, D. & Larson, D.J. (2014). Developing detection efficiency standards for atom probe tomography. Proc SPIE 9173, 917307.
Prosa, T.J., Lawrence, D., Olson, D., Larson, D.J. & Marquis, E.A. (2009). Backside lift-out specimen preparation: Reversing the analysis direction in atom probe tomography. Microsc Microanal 15(S2), 298299.
Qu, J., Wong, D., Du, S., Yang, L., Ringer, S. & Zheng, R. (2015). Methodology exploration of specimen preparation for atom probe tomography from nanowires. Ultramicroscopy 159(Pt 2), 427431.
Rice, K.P., Chen, Y., Prosa, T.J. & Larson, D.J. (2016). Implementing transmission electron backscatter diffraction for atom probe tomography. Microsc Microanal 22, 583588.
Rice, K.P., Chen, Y., Prosa, T.J., Larson, D.J., Nowell, M. & Stoykovich, M.P. (2015). Techniques for transmission EBSD mapping of atom probe specimens. Microsc Microanal 21(S3), 16771678.
Rice, K.P., Keller, R.R. & Stoykovich, M.P. (2014). Specimen-thickness effects on transmission Kikuchi patterns in the scanning electron microscope. J Microsc 254, 129136.
Riley, J.R., Padalkar, S., Li, Q., Lu, P., Koleske, D.D., Wierer, J.J., Wang, G.T. & Lauhon, L.J. (2013). Three-dimensional mapping of quantum wells in a GaN/InGaN core–shell nanowire light-emitting diode array. Nano Lett 13, 43174325.
Sanford, N.A., Blanchard, P.T., Brubaker, M., Bertness, K.A., Roshko, A., Schlager, J.B., Kirchhofer, R., Diercks, D.R. & Gorman, B. (2014). Laser-assisted atom probe tomography of MBE grown GaN nanowire heterostructures. Phys Status Solidi C 11, 608612.
Seto, K., Larson, D.J., Warren, P.J. & Smith, G.D.W. (1999). Studies of grain boundaries of B-doped interstitial-free steels on the atomic scale by three-dimensional atom probe. Scipta Mater 40, 1029.
Shimizu, Y., Kawamura, Y., Uematsu, M., Tomita, M., Kinno, T., Okada, N., Kato, M., Uchida, H., Takahashi, M., Ito, H., Ishikawa, H., Ohji, Y., Takamizawa, H., Nagai, Y. & Itoh, K.M. (2011). Depth and lateral resolution of laser-assisted atom probe microscopy of silicon revealed by isotopic heterostructures. J Appl Phys 109, 36102.
Smith, G.D.W. (2016). Private communication.
Stadermann, F.J., Isheim, D., Zhao, X., Daulton, T.L., Floss, C., Seidman, D.N., Heck, P.R., Pellin, M.J., Savina, M.R., Hiller, J., Mane, A., Elam, J., Davis, A.M., Stephan, T. & Amari, S. (2011). Atom-probe tomographic characterization of meteoritic nanodiamonds and presolar SiC. In 42nd Lunar and Planetary Science Conference, The Woodlands, Texas. Submission 1595.
Taheri, M.L., Sebastian, J.T., Reed, B.W., Seidman, D.N. & Rollett, A.D. (2010). Site-specific atomic scale analysis of solute segregation to a coincidence site lattice grain boundary. Ultramicroscopy 110, 278284.
Takahashi, J., Kawakami, K. & Kobayashi, Y. (2014). In situ determination of misorientation angle of grain boundary by field ion microscopy analysis. Ultramicroscopy 140, 2025.
Takamizawa, H., Shimizu, Y., Nozawa, Y., Toyama, T., Morita, H., Yabuuchi, Y., Ogura, M. & Nagai, Y. (2012). Dopant characterization in self-regulatory plasma doped fin field-effect transistors by atom probe tomography. Appl Phys Lett 100, 93502.
Thompson, G.B., Genc, A., Morris, R., Torres, K.L. & Fraser, H.L. (2009). Correlation between TEM imaging and microanalysis for atom probe reconstruction verification. Microsc Microanal 15(S2), 250251.
Thompson, K., Gorman, B.P., Larson, D.J., van Leer, B. & Hong, L. (2006). Minimization of Ga induced FIB damage using low energy clean-up. Microsc Microanal 12, 1736CD.
Thompson, K., Larson, D.J. & Ulfig, R. (2005). Pre-sharpened and flat-top microtip coupons: A quantitative comparison for atom-probe analysis studies. Microsc Microanal 11(S2), 882.
Thompson, K., Lawrence, D.J., Larson, D.J., Olson, J.D., Kelly, T.F. & Gorman, B. (2007). In-situ site-specific specimen preparation for atom probe tomography. Ultramicroscopy 107, 131139.
Trimby, P.W. (2012). Orientation mapping of nanostructured materials using transmission Kikuchi diffraction in the scanning electron microscope. Ultramicroscopy 120, 1624.
Vasile, M.J., Grigg, D., Griffith, J.E., Fitzgerald, E. & Russell, P.E. (1991). Scanning probe tip geometry optimized for metrology by focused ion beam ion milling. J Vac Sci Technol 9, 35693572.
Vurpillot, F., Larson, D. & Cerezo, A. (2004). Improvement of multilayer analyses with a three-dimensional atom probe. Surf Interface Anal 36, 552558.
Waugh, A.R., Bayly, A.R. & Anderson, K. (1984a). The application of liquid metal ion sources to SIMS. Vacuum 34, 103.
Waugh, A.R., Payne, S., Worrall, G.M. & Smith, G.D.W. (1984b). In situ ion milling of field ion specimens using a liquid metal ion source. J Phys 45, 207209.
Xiong, X. & Weyland, M. (2014). Microstructural characterization of an Al-Li-Mg-Cu alloy by correlative electron tomography and atom probe tomography. Microsc Microanal 20, 10221028.
Xu, T., Nys, J.P., Grandidier, B., Stiévenard, D., Coffinier, Y., Boukherroub, R., Larde, R., Cadel, E. & Pareige, P. (2008). Growth of Si nanowires on micropillars for the study of their dopant distribution by atom probe tomography. J Vac Sci Technol B 26, 19601963.
Yao, L. & Miller, M.K. (2013). Direct experimental measurement of Grain boundary’s five-parameters and solute segregations at atomic level. Microsc Microanal 19(S2), 938939.

Keywords

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed