Moonsub Shim

The overarching goal of our research program is to develop novel nanoscale materials and understand charging and charge separation phenomena occurring in them. Charging and charge separation are fundamental processes that govern how electronic, optoelectronic, and photovoltaic devices operate. Materials with nanometer dimensions provide new engineering paradigms and prospects for devices with unprecedented performance. However, ubiquitously large surface-to-volume ratio of materials in this size regime often leads to large deviations from the expected and therefore difficulties arise in achieving the desired performance. The ability to control surface and interfacial effects is then critical in elucidating the underlying materials’ properties which in turn is essential in developing any future technologies. Hence, we study how charging and charge separation processes affect structure, electrical and optical properties, and chemical reactivity with special attention to the materials’ responses to variations at surfaces and interfaces. Insights gained from these studies are then exploited to develop new materials exhibiting superior properties useful for solar energy conversion and high performance nano- and macro-electronics. 

With continuing scale down of electronic devices, increasing influence of the surface and interactions with the surrounding environment are inevitable and often present a major challenge. From device performance limits to thermal management, understanding how such extrinsic factors affect fundamental processes such as charging, electron-phonon coupling and energy relaxation/dissipation is fundamentally important. Due to their atomic thickness, carbon nanotubes and graphene are interesting platforms to examine how local chemical environments affect these fundamental processes. Such studies, in turn, may provide effective means of controlling device characteristics. By examining and controlling “hetero” interfaces of low-dimensional graphitic carbon with substrates and other surrounding media, we are developing new routes to integrating them into next generation electronics.

High quality epitaxial heterointerfaces and delicately controlled shape anisotropy can be achieved with versatile and scalable wet chemical synthesis of semiconductor nanocrystal heterostructures. Such heterostructures with tunable electronic structure and anisotropic shapes are being developed in our laboratory. Their band gaps, band offsets and the resulting optical and electrical properties are tunable through quantum confinement, composition and lattice strain effects. Anisotropic shapes are especially useful as they provide directionality in extracting/injecting carriers. These salient features of anisotropic nanocrystal heterostrctures are being exploited to develop high performance optoelectronics and photovoltaics.

Carbon Nanoelectronics

Nanocrystal Heterostructures

A complete list can be found at: http://shimlab.matse.illinois.edu/publication.html

H. McDaniel, P. E. Heil, C. -L. Tsai, K. Kim, and M. Shim, “Integration of Type II Nanorod Heterostructures into Photovoltaics,” ACS Nano, accepted (2011).

C. –L. Tsai, A. Liao, E. Pop, and M. Shim, “Electrical Power Dissipation in Carbon Nanotubes on Single Crystal Quartz and Amorphous SiO2,” Appl. Phys. Lett.  99, 053120 (2011).

H. McDaniel, J. –M. Zuo, and M. Shim, “Anisotropic Strain Induced Curvature in Type II CdSe/CdTe Nanorod Heterostructures,”J. Am. Chem. Soc. 132, 3286 – 3288 (2010).

J. H. Back, C. –L. Tsai, S. Kim, S. Mohammadi, and M. Shim, “Manifestation of Kohn Anomaly in 1/f Fluctuations in Metallic Carbon Nanotubes,” Phys. Rev. Lett. 103, 215501 (2009).

K. T. Nguyen and M. Shim, “Role of covalent defects on phonon softening in metallic carbon nanotubes,”  J. Am. Chem. Soc. 131, 7103 (2009).

H. McDaniel and M. Shim, “Size and Growth Rate Dependent Structural Diversification of Fe3O4/CdS Anisotropic Nanocrystal Heterostructures,” ACS Nano 3, 434 (2009).

D. Abdula and M. Shim, “Performance and Photovoltaic Response of Polymer Doped Carbon Nanotube p-n Diodes,” ACS Nano 2, 2154 (2008).

Q. Cao, H.- S. Kim, N. Pimparkar, J. P. Kulkarni, C. Wang, M. Shim, K. Roy, M. A. Alam, J. A. Rogers, “Medium Scale Carbon Nanotube Thin Film Integrated Circuits on Flexible Plastic Substrates,” Nature 454, 495 (2008).

K. T. Nguyen, A. Gaur, and M. Shim, “Fano Lineshape and Phonon Softening in Single Isolated Metallic Carbon Nanotubes,” Phys. Rev. Lett. 98, 145504 (2007).

S. J. Kang, C. Kocabas, T. Ozel, M. Shim, N. Pimparkar, A. Alam, S. V. Rotkin, and J. A. Rogers, “High Performance Electronics Based on Dense, Perfectly Aligned Arrays of Single Walled Carbon Nanotubes,” Nature Nanotech., 2, 230 – 236 (2007).

K. –W. Kwon, B. H. Lee, and M. Shim, “Structural Evolution in Metal Oxide/Semiconductor Colloidal Nanocrystal Heterostructures,” Chem. Mater. 18, 6357 – 6363 (2006).

M. Shim, T. Ozel, A. Gaur, and C. Wang, “Insights on Charge Transfer Doping and Intrinsic Phonon Line Shape of Carbon Nanotubes by Simple Polymer Adsorption,” J. Am. Chem. Soc. 128, 7522– 7530 (2006).

C. Kocabas, M. Shim, and J. A. Rogers, “Spatially Selective Guided Growth of High-Coverage Arrays and Random Networks of Single-Walled Carbon Nanotubes and Their Integration into Electronic Devices,”  J. Am. Chem. Soc. 128, 4540 – 4541 (2006).

C. Wang, Q. Cao, T. Ozel, A. Gaur, J. A. Rogers, and M. Shim, “Electronically Selective Chemical Functionalization of Carbon Nanotubes: Correlation between Raman Spectral and Electrical Responses,” J. Am. Chem. Soc. 127, 11460 – 11468 (2005).

K. –W. Kwon and M. Shim, “g-Fe2O3/II-VI Sulfide Nanocrystal Heterojunctions,” J. Am. Chem. Soc, 127, 10269 – 10275 (2005).

T. Ozel, A. Gaur, J. A. Rogers, and M. Shim, “Polymer Electrolyte Gated Carbon Nanotube Network Transistors,” Nano Lett. 5, 905 – 911 (2005).

G. P. Siddons, D. Merchin, J. H. Back, J. K. Jeong, and M. Shim, “Highly Efficient Gating and Doping of Carbon Nanotubes with Polymer Electrolytes,” Nano Lett. 4, 927 – 931 (2004).

M. Shim and G. P. Siddons, “Photoinduced Conductivity Changes in Carbon Nanotube Transistors,”  Appl. Phys. Lett. 83, 3564 – 3566 (2003).

• Elizabeth R. Norton Prize, U. of Chicago (2000)
• Racheff Assistant Professor (2002-2004)
• NSF CAREER Award (2004)
• Xerox Award for Faculty Research (2007)
• Willett Faculty Scholar (2010-)