Professor, Department of Physics & Astronomy
Location: 4213 Biomed Phys Sci
My research is in the area of condensed matter experiments with emphasis on understanding the fundamental properties of low-dimensional electronic and photovoltaic materials using scanning probe microscopy in conjunction with device characterization, and furthermore manipulating the properties of these low-dimensional materials and devices via surface and interface engineering. The ability to control the synthesis of low-dimensional materials and heterostructures has the potential to revolutionize technology. On the one hand, the utility of these engineered low-dimensional materials for important applications such as energy conversion and storage devices, nanoscale electronics, and molecular/biological sensors has in many cases been severely limited by interfacial phenomena that emerge at the nanoscale. On the other hand, new functionalities and exotic behaviors that are not accessible in individual constituents may arise from interfacial proximity coupling when materials of different properties are integrated into heterostructures. It is thus crucial to develop a thorough atomic- and molecular- level understanding and a precise control of surfaces and interfaces. We have extensively studied the molecular self-assembly process, a powerful technique to manufacture and organize nanoscale structures, and made the first observation of long-ranged ordered step-flow growth in organic thin films. Access to this growth mode offers the potential for improved performance in organic electronic and energy harvesting devices. Combining comprehensive scanning probe studies and device characterizations, we revealed the heterogeneous behaviors of grain boundaries and their impacts on the performance of high-efficiency perovskite solar cells. One of our current research interests is to investigate organic charge transfer complex (CTCs) thin films composed of donor and acceptor molecular moieties. Aided by the construction of heterostructures using bottom-up approach, we established a microscopic understanding of the crucial physics occurring near[photo of Dr. Zhang lab] boundaries of mixed valence and its impacts on insulator-to-metal transition in an organic CTC. Recently, we also demonstrated a novel technique to induce the phase transformation in two-dimensional transition metal dichalcogenides (TMDs) from conventional semiconductor to topological insulator via construction of core-shell lateral heterostructures. This finding offers a possible route for rational design of heterostructure with target functionalities. # Education: * 2006: Ph.D., University of Wisconsin, Madison * 2000: M.S., Beijing Normal University * 1997: B.S., Beijing Normal University
- PHY 431: Optics I
- A. Tan, and P. P. Zhang, "Tailoring the Growth and Electronic Structures of Organic Molecular Thin Films", J. Phys.: Condens. Matter, 31, 503001 (2019).
- A. Tan, S. R. Wagner, and P. P. Zhang, "Electrostatic Screening Mediated by Interfacial Charge Transfer in Molecular Assemblies on Semiconductor Substrates", Phys. Rev. B, 96, 035313 (2017).
- C. Jiang, and P. P. Zhang, "Crystalline Orientation Dependent Photoresponse and Heterogeneous Behaviors of Grain Boundaries in Perovskite Solar Cells", J. Appl. Phys., 123, 083105 (2018).
- J. Feng, A. Tan, S. R. Wagner, J. Liu, Z. Mao, X. Ke, and P. P. Zhang, "Charge Modulation and Structural Transformation in TaTe2 Studied by Scanning Tunneling Microscopy/Spectroscopy", Appl. Phys. Lett. 109, 021901 (2016).
- S. R. Wagner, B. Huang, C. Park, J. Feng, M. Yoon, and P. P. Zhang, "Growth of Metal Phthalocyanine on Deactivated Semiconducting Surfaces Steered by Selective Orbital Coupling", Phys. Rev. Lett. 115, 096101 (2015).
- X. Dong, W. Lai, and P. P. Zhang, "Semiconductor to Topological Insulator Transition Induced by Stress Propagation in Metal Dichalcogenide Core-Shell Lateral Heterostructures", Mater. Horiz. 8, 1029 (2021).
- X. Dong, Y. Hu, S. Ren, and P. P. Zhang, "Spatially Resolved Investigation of Mixed Valence and Insulator-to-Metal Transition in an Organic Salt", J. Phys. Chem. Lett. 11, 8352 (2020).