A. J. Mannix, B. Kiraly, M. C. Hersam, and N. P. Guisinger, “Synthesis and chemistry of elemental 2D materials,” Nature Reviews Chemistry, 1, 0014 (2017).
The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. Given that any passivated, dangling-bond-free surface will interact with another through vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through non-covalent interactions. We present a succinct and critical survey of emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices. By comparing and contrasting with all-2D vdW heterostructures as well as with competing conventional technologies, we highlight the challenges and opportunities for mixed-dimensional vdW heterostructures.
D. Jariwala, T. J. Marks, and M. C. Hersam, “Mixed-dimensional van der Waals heterostructures,” Nature Materials, 16, 170 (2017).
Layer-by-layer assembled 2D montmorillonite nanosheets are shown to be high-performance, solution-processed dielectrics. These scalable and spatially uniform sub-10 nm thick dielectrics yield high areal capacitances of ≈600 nF cm−2 and low leakage currents down to 6 × 10−9A cm−2 that enable low voltage operation of p-type semiconducting single-walled carbon nanotube and n-type indium gallium zinc oxide field-effect transistors.
J. Zhu, X. Liu, M. L. Geier, J. J. McMorrow, D. Jariwala, M. E. Beck, W. Huang, T. J. Marks, and M. C. Hersam, “Layer-by-Layer Assembled 2D Montmorillonite Dielectrics for Solution-Processed Electronics,” Adv. Mater., 28, 63 (2016).
S. Jang, B. Kim, M. L. Geier, M. C. Hersam, and A. Dodabalapur, “Short channel field-effect-transistors with inkjet-printed semiconducting carbon nanotubes,” Small, 11, 5505 (2015).
Scanning Probe Microscopy
We utilize a diverse array of scanning probe techniques to grow, analyze and manipulate nanomaterials on the atomic and molecular scale. Using ultra-high vacuum scanning tunneling microscopy, we have explored electronic transport in organic molecules on a surface, investigated the surface chemistry and functionalization of graphene, and characterized the electronic properties of novel two-dimensional materials. Our lab continues to expand the boundaries of our scanning probe capabilities by utilizing various variations of atomic force microscopy, expanding our ultra-high vacuum growth and characterization capabilities, and applying novel techniques, such as tip-enhanced Raman spectroscopy, to push the limits of fundamental surface science.
X. Liu, I. Balla, H. Bergeron, G. P. Campbell, M. J. Bedzyk, and M. C. Hersam, “Rotationally commensurate growth of MoS2 on epitaxial graphene,” ACS Nano,10, 1067 (2016).
A. J. Mannix, X.-F. Zhou, B. Kiraly, J. D. Wood, D. Alducin, B. D. Myers, X. Liu, B. L. Fisher, U. Santiago, J. R. Guest, M. J. Yacaman, A. Ponce, A.R. Oganov, M. C. Hersam, and N. P. Guisinger, “Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs,” Science, 350, 1513 (2015).
B. Kiraly, E. V. Iski, A. J. Mannix, B. L. Fisher, M. C. Hersam, and N. P. Guisinger, “Solid-source growth and atomic-scale characterization of graphene on Ag(111),” Nature Comm., 4, 2804 (2013).
Md. Z. Hossain, J. E. Johns, K. H. Bevan, H. J. Karmel, Y. T. Liang, S. Yoshimoto, K. Mukai, T. Koitaya, J. Yoshinobu, M. Kawai, A. M. Lear, L. L. Kesmodel, S. L. Tait, and M. C. Hersam, “Chemically homogeneous and thermally reversible oxidation of epitaxial graphene,” Nature Chemistry, 4, 305 (2012).
Q. H. Wang and M. C. Hersam, “Room-temperature molecular-resolution characterization of self-assembled organic monolayers on epitaxial graphene,” Nature Chemistry, 1, 206 (2009).
N. P. Guisinger, N. L. Yoder, and M. C. Hersam, “Probing charge transport at the single molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy,” Proc. Nat. Acad. Sci. USA, 102, 8838 (2005).
Our lab utilizes density gradient ultracentrifugation to sort various polydisperse nanomaterials into monodisperse solutions by a wide variety of parameters. We have previously demonstrated sorting of single-walled carbon nanotubes by electronic type, chirality, diameter, and handedness as well as sorting double-walled carbon nanotubes by their outer shell. We continue to extend our techniques to sort 2D nanomaterials, such as graphene, hexagonal boron nitride, and molybdenum disulfide, as well as anisotropic, polydisperse metallic nanoparticles. Additionally, our lab has developed methods for producing and tailoring functional nanomaterial inks for integration in printed electronics. The broad expertise in solution-phase processing of nanomaterials also enables studies of their biological toxicity and potential applications in drug delivery.
J. Zhu, J. Kang, J. Kang, D. Jariwala, J. D. Wood, J.-W. T. Seo, K.-S. Chen, T. J. Marks, and M. C. Hersam, “Solution-processed dielectrics based on thickness-sorted two-dimensional hexagonal boron nitride nanosheets,” Nano Lett., 15, 7029 (2015).
J. Kang, J. D. Wood, S. A. Wells, J.-H. Lee, X. Liu, K.-S. Chen, and M. C. Hersam, “Solvent exfoliation of electronic-grade, two-dimensional black phosphorus,” ACS Nano, 9, 3596 (2015).
E. B. Secor, B. Y. Ahn, T. Z. Gao, J. A. Lewis, and M. C. Hersam, “Rapid and versatile photonic annealing of graphene inks for flexible printed electronics,” Adv. Mater., 27, 6683 (2015).
J. Kang, J.-W. T. Seo, D. Alducin, A. Ponce, M. J. Yacaman, and M. C. Hersam, “Thickness sorting of two-dimensional transition metal dichalcogenides via copolymer-assisted density gradient ultracentrifugation,” Nature Comm., 5, 5478 (2014).
A. A. Green and M. C. Hersam, “Solution phase production of graphene with controlled thickness via density differentiation,” Nano Letters, 9, 4031 (2009).
M. S. Arnold, A. A. Green, J. F. Hulvat, S. I. Stupp, and M. C. Hersam, “Sorting carbon nanotubes by electronic structure via density differentiation,” Nature Nanotechnology, 1, 60 (2006).
Nanoscale Devices for Electronics and Energy
The ever-changing energy needs of our society necessitate the exploration of novel methods of energy collection and storage. Towards this goal, we utilize our expertise in processing nanomaterials to explore applications of carbon nanotubes, graphene, and related two-dimensional materials for energy generation and storage. Advanced electronic and chemical characterization techniques provides deep insight into these systems, with key examples including impedance spectroscopy for photovoltaics and scanning conductive ion microscopy for lithium ion batteries. Such techniques offer a better understanding of the key issues in enabling practical applications of these technologies.
Our nanomaterials processing and electrical characterization work allows us to push the limits of nanoscale electronic devices. By uniting high-performance electronic nanomaterials, robust fabrication techniques, and detailed electrical characterization we have demonstrated large-scale complementary carbon nanotube electronics, along with novel gate-tunable devices including memristors and p-n heterojunctions.
M. L. Geier, J. J. McMorrow, W. Xu, J. Zhu, C. H. Kim, T. J. Marks, and M. C. Hersam, “Solution-processed carbon nanotube thin-film complementary static random access memory,” Nature Nanotechnology, 10, 944 (2015).
L. Jaber-Ansari, K. P. Puntambekar, S. Kim, M. Aykol, L. Luo, J. Wu, B. D. Myers, H. Iddir, J. T. Russell, S. J. Saldaña, R. Kumar, M. M. Thackeray, L. A. Curtiss, V. P. Dravid, C. Wolverton, and M. C. Hersam, “Suppressing manganese dissolution from lithium manganese oxide spinel cathodes with single-layer graphene,” Adv. Energy Mater., 5, 1500646 (2015).
V. K. Sangwan, D. Jariwala, I. S. Kim, K.-S. Chen, T. J. Marks, L. J. Lauhon, and M. C. Hersam, “Gate-tunable memristive phenomena mediated by grain boundaries in single-layer MoS2,” Nature Nanotechnology, 10, 403 (2015).
M. Gong, T. A. Shastry, Y. Xie, M. Bernardi, D. Jasion, K. A. Luck, T. J. Marks, J. C. Grossman, S. Ren, and M. C. Hersam, “Polychiral semiconducting carbon nanotube-fullerene solar cells,” Nano Lett., 14, 5308 (2014).
D. Jariwala, V. K. Sangwan, C.-C. Wu, P. L. Prabhumirashi, M. L. Geier, T. J. Marks, L. J. Lauhon, and M. C. Hersam, “Gate-tunable carbon nanotube-MoS2 heterojunction p-n diode,” Proc. Nat. Acad. Sci. USA, 110, 18076 (2013).
V. K. Sangwan, R. P. Ortiz, J. M. P. Alaboson, J. D. Emery, M. J. Bedzyk, L. J. Lauhon, T. J. Marks, and M. C. Hersam, “Fundamental performance limits of carbon nanotube thin-film transistors achieved using hybrid molecular dielectrics,” ACS Nano, 6, 7480 (2012).