Topology, best understood for weakly interacting electrons, implies robust protection ofelectronic properties. Magnetism, on the other hand, arises fundamentally from strong interactions. An urgent and tantalizing question is whether topological protection can arise in magnetic systems, since achieving precise control over the magnetic properties of solids is a long-standing problem with critical applications for both spintronics and quantum information. IRG-2 seeks to establish a new paradigm for topological phases in strongly correlated magnetic materials.

• IRG-2’s materials synthesis and crystal growth programs will generate a new class of magnetic materials for the condensed matter community, with great potential impacts on science and our national competitiveness.

• New algorithms and software developed within this proposal to search for topological magnetic materials will be internet accessible, leading to improvements in the computer-aided design of materials in physics, chemistry, and materials communities.

• All members of IRG-2 will engage fully in CEM diversity and outreach programs. Valdés-Aguilar, the CEM REU Director and Bridge Program steering committee member, and Trivedi, the faculty lead of the Scientific Thinkers program, will take leadership roles. Also, during the course of the work, they plan to include these topics in a CEM organized international conference.

The University of Pennsylvania Materials Research Science & Engineering Center (MRSEC) will build on past success and embrace new faculty to pursue a program to integrate the design, synthesis, characterization, theory & modeling of materials. These materials range from hybrid macro-molecules and de novo proteins, with architectures & functions inspired by nature, to nano- and micro-structured hard & soft materials with unique properties. Potential practical outcomes are in the areas of drug delivery, energy transduction, electronics, sensors, and cellular probes. The MRSEC research is organized around five Interdisciplinary Research Groups (IRGs), which target new advanced materials with potential for high-technology applications in diverse areas such as energy transduction, electronics, sensors, & cellular probes. Materials interfaces are a recurrent theme, as is the interplay between biological & synthetic constructs and composites of hard & soft materials. The MRSEC sustains an array of education and human resources development programs, whose impact will range from K-12 students and their teachers to undergraduates and faculty at minority serving institutions. It is associated with the University of Puerto Rico at Humacao through a Partnership for Research and Education in Materials (PREM). The MRSEC manages extensive shared facilities that benefit the broader research community. The MRSEC is linked with Penn's Center for Technology Transfer to license its discoveries and inventions for translational research thereby ensuring the coupling of MRSEC research to the needs of society.

The MRSEC contains the following IRGs: Filamentous Networks and
Structured Gels, IRG-1 explores the properties of filamentous networks with a goal to design & synthesize responsive network materials. Functional Cylindrical Assemblies, IRG-2 will synthesize semi-flexible, functional cylinders, composed of dendrimer-based polymers & self-assembling block copolymers. Synthetic Programmable Membranes, IRG-3 draws expertise from four departments to design fully integrated functional analogues of cellular membranes. De Novo Synthetic Protein Modules for Light-Capture & Catalysis, IRG-4 draws on the rich biological resource of atomic-level structures and functional mechanisms to guide design & synthesis of novel proteins as modular nano-scale materials. Oxide-based Hierarchical Interfacial Materials, IRG-5 will harness expertise in theory, synthesis, & experiment, from four departments to create and understand novel hierarchical interfacial oxide materials.

IRG-1 aims to develop functional low-dimensional materials that harness cross-coupling between photons and electron spins — spin-photonic nanostructures — to enable future classical and quantum information processing, sensing, and photonics technologies, such as spin-photonic transduction, Faraday optical isolation, and quantum memory.

By addressing fundamental issues related to soft, LC-based materials on multiple length scales via the integration of complementary experimental and theoretical tools, IRG 3 provides a foundation of knowledge with broad potential for impact on the design of hierarchical and active soft materials. Key fundamental issues IRG 3 investigates include the equilibrium and the non-equilibrium, dynamic behaviors of molecules at interfaces of anisotropic soft materials, interfacial ionic phenomena in LC systems, dynamic mechanical and transport properties of several classes of LC gels, including concepts of molecular frustration and surface-driven ordering transitions, and the structure and energetics of the cores of LC defects, including cores that host adsorbates. The challenge of designing these complex LC material systems is addressed by IRG 3 through the development of new experimental techniques, multi-scale theory and simulation, and new methods of synthesis and processing.

This IRG develops new heteroanionic materials with tunable electronic, ionic, thermal, and optical properties, which are otherwise inaccessible from simpler homoanionic structures and chemistries. Discovery of heteroanionic materials are facilitated by synthetic and characterization methods that provide a panoramic view of crystallization and diffusion processes in which emerging phases of interest are revealed and growth mechanisms are delineated. By emphasizing synthesis as the central science, the tools, protocols, and databases formulated in IRG-2 enable synthesis-on-demand of complex materials suggested by computational discovery.

IRG 2 explores the principles governing condensed protein mesophases and cell collectives to engineer dynamic biomaterials. By leveraging bioinspired design, the team develops synthetic structures with applications in biotechnology, medicine, and materials science, spanning scales from microns to centimeters.

IRG Senior Participants: Paul McEuen (co-leader, Phys), Jiwoong Park (co-leader, C&CB), Garnet Chan (C&CB), Harold Craighead (A&EP), Richard Hennig (MS&E), Jeevak Parpia (Phys), Keith Schwab (Phys), Michael Spencer (E&CE) Collaborators: N. Sepulveda-Alancastro (U. of Puerto Rico at Mayag??ez), K. Ekinci (Boston Univ.), P. Kim (Columbia Univ.), B. Lane (Analog Devices), M. Zalalutdinov (NRL)

Our group is exploring the properties of atomic membranes: mechanically robust, freestanding films of material as thin as a single atom. The prototypical example is graphene, a single sheet of graphite. We are examining the mechanical, thermal, optical, and electronic properties of this novel material, as well as studying the effect of individual defects and adsorbates on it. In addition, we are using these membranes as an atomically thin interface between different environments, such as gas/vacuum or liquid/gas. This unprecedented ability to put different phases in nanoscale proximity, separated by only an atomically-thin wall, makes possible a wealth of new nanoscale measurements.

The primary objective of IRG-4 is to improve fundamental understanding, optimize process efficiency, and enable novel technological advances across multiple length-scales of hybrid organic-inorganic materials for nanoelectronic applications. Two major themes organize the group's efforts to realize new design principles and paradigms for electronic materials.

Materials Design: IRG-4 integrates theory and experiment to develop deep understanding of structure-electronic property relationships from the molecular scale to the macro scale. This understanding is employed to advance and optimize organic conductors and dielectrics and open up new vistas in the design of hybrid materials for nanoelectronic applications.

Materials Integration: IRG-4 pursues fundamental chemical and structural understandings of the interfaces between organic and inorganic materials including nanowires, nanotubes, and graphene, leading to advances in interface engineering and processing that are enabling for novel hybrid materials and technologies.

Accomplishments include:

• The theoretically guided design and synthesis of new organic high dielectrics and inorganic semiconductor nanowire heterostructures.
• Processing of  single-walled carbon nanotubes into metallic  transparent conducting contacts and semiconducting thin film transistors.
• Integration of molecular semiconductors, organic dieletrics, and inorganic nanowires into printable electronics.
• Spatially resolved electrical characterization of inorganic nanowires correlated with atomic-scale dopant mapping.
• New theories of non-equilibrium transport and quantum electronic structure of molecular materials and molecules at interfaces.

Hydrogels are extensively used in medical applications and they are an important class of biomaterials that are under significant study for regenerative medicine applications. They are cross-linked, three-dimensional, hydrophilic polymer networks that can swell but not dissolve in water. Hydrogels derived from biological macromolecules such as proteins and polysaccharides are of great interest to the biomedical community as they can contain intrinsic biological information or serve as an extracellular matrix mimic. The study of the properties of functional and responsive hydrogels presents a fundamental challenge with important practical applications. What are the molecular factors that determine the structure of the gel? What is the activity of specific ligands within the gel? How do pH sensitive groups respond within the network structure? In order to study these complex systems we are carrying out a combined experimental and theoretical effort aimed at the fundamental understanding of the mechanism of formation and properties of hydrogels formed by mixtures of proteins and polymers. We have developed a novel family of water-soluble poly(diol citrates) that can mediate the formation of a protein gel via complexation. Protein-polymer gels with water content of up to 90% have been fabricated with bovine and human serum albumin, fibrinogen, and hemoglobulin without covalently modifying the protein. The gels can form within 10 minutes, depending on the protein and temperature of the gelation and degrade within 4 to 8 weeks. The overall objectives of this project include the understanding at the fundamental level of the driving forces for the formation of this class of hydrogels, the mechanism of gel formation and the identification of design criteria that would allow the formation of the protein gels for tissue engineering applications. Toward this goal, we are using a combination of theoretical studies and experimental observations to investigate the formation and properties of the gels as well as the feasibility of using these protein gels for controlled release of proteins and cell encapsulation. The results of this research will lead to a new paradigm on the mechanism for protein gel formation and protein delivery.

Among common semiconductor devices are the diode, field effect transistor, and bipolar junction transistor (BJT). Thin-film analogues of the first two exist and enable commercial products, such as flexible displays and thin-film solar cells. The thin-film BJT has, however, been elusive. Inorganic semiconductor processing steps for deposition and doping required for BJTs are ill-suited for making thin-film BJTs.  On the other hand, the ability to deposit organic semiconductor films at low temperature, control their thickness down to the nm range, engineer interfaces with well-defined energy structures, and chemically dope the films should allow for fabricating and demonstrating a thin-film BJT.

The Seed 2 project aims at investigating the interplay between doped organic molecular films, with the ultimate goal of fabricating and testing p-n type heterojunctions that are central to an organic BJT.  Central issues for the realization of molecular BJTs are the controlled n- and p-type doping of the emitter, base and collector sections of the device, and the transport of carriers via diffusion through the base. Carrier transport in molecular films is negatively impacted by disorder-, defect- and impurity-induced electronic traps and tail gap states, which decrease mobility and act as recombination centers.  In our project, chemical n- and p-doping not only serves to establish the p-n-p (or n-p-n) structure of a BJT, but is also used to passivate, or de-activate, these traps and gap states, thereby improving transport.

Principal Investigators
Barry Rand (Electrical Engineering)
Antoine Kahn (Electrical Engineering; Engineering and Applied Science) 

* This seed is inactive.