Dr. Robinson’s interests span a wide range of electronic materials capable of integration into many different technologies.  However, materials for electronic and optoelectronic, as well as and radiation detection have become a prime focus of his research. 

One such material is “graphene” – a single sheet of graphite. Graphene presents a host of remarkable physical and chemical properties, many of which originate from its special electronic band structure. For instance, the mobility of the charge carriers in graphene is as high as ~ 200,000 cm2/Vs even when the carrier density is 1013 cm-2, making graphene a very attractive material for high speed (RF & terra-hertz) electronic applications.  Realization of a graphene technology; however, requires the ability to synthesize high quality graphene, rapidly characterize the material’s structural and electronic quality, and integrate graphene with dielectric materials for device fabrication. Dr. Robinson initiated a graphene research effort in the fall of 2007 at the PSU-EOC with the goals of making graphene a producible material for integration into high speed electronics, and has worked with PSU-EOC researchers to produce the world’s largest graphene wafer to date (100mm). Additionally, Dr. Robinson has developed graphene device fabrication processes for record performance, high speed transistors. In addition to graphene, Dr. Robinson is actively engaged in research on developing synthesis, characterization, and integration techniques of “beyond graphene” materials. These material systems include 2D material systems such as hexagonal boron nitride (hBN), as well as transition-metal dichalcogenides in the form of MX2 (where M=transition metal such as Mo, W, Ti, Nb, etc. and X=S, Se, or Te). 

Finally, Dr. Robinson is also actively engaged in materials development for radiation detection. This work includes use of rare-earth oxide materials such as gadolinium that produces a charge when radiation is incident on the material.  Additionally, Dr. Robinson is pursuing the integration of multiple 2D material systems such as hexagonal boron nitride for flexible radiation detection applications.

Research efforts are focused on the growth and characterization of oxide thin films. This class of materials has an unparalleled spectrum of physical properties which makes them very interesting for a variety of applications ranging from energy generation, sensors and actuators to memory and logic device concepts.  The monolithic integration of oxide thin films to cross-couple different functionalities, novel interface phenomena, epitaxial stabilization of unfavorable phases and strain engineering provide additional degrees of freedom that are largely unexplored, which further extend the opportunities to tailor material properties. Although oxide films can be grown with high structural perfection, intrinsic material properties might be obscured by a high level of unintentional defects.
Molecular beam epitaxy (MBE) is the main synthesis method employed by this group. The system design facilitates the deposition of metal organic molecules and thus combines low energetic deposition techniques in a unique way, dubbed "Hybrid MBE". Stoichiometric control and suppression of defect formation during growth as well as doping strategies are addressed. Structural characterization methods encompass X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Hall measurements and admittance spectroscopy are used for electrical characterization.
Another research area are magnetic domain structures in confined geometries with nanoscale dimensions. Domain arrangements, their formation and stability in the presence of an external magnetic field are studied by magnetic force microscopy. Current induced magnetization dynamics, such as spin transfer torque magnetization reversal and domain wall motion, are investigated using micromagnetic simulation. Magnetic nanostructures are building blocks of spin-electronic devices and the study of these phenomena is imperative for their successful application in the area of information technology.

Dr. Redwing’s research interests lie in the general area of electronic and optoelectronic materials synthesis and characterization with a special emphasis on chemical vapor deposition processing of semiconductor thin films and nanostructures. A current area of research focuses on the growth of semiconductor nanowires utilizing a combination of templating and directed growth techniques. This work is aimed at understanding the fundamental mechanisms of nanowire growth and the impact of nanoscale phenomena on materials synthesis. The fabrication of radial and axial nanowire heterostructures and p-n junctions is also under investigation for nanoscale device development. This research is an integral part of several multidisciplinary research team projects at Penn State which are focused on the development of nanowire-based devices for applications in microelectronics, chemical and biological sensing and solar energy conversion. The deposition of wide bandgap group III-nitride ((Al,Ga,In)N) thin films by metalorganic chemical vapor deposition is another active area of research. These materials are used in a wide variety of electronic and optoelectronic devices including high brightness light emitting diodes used in solid state lighting and high frequency/high power transistors for radar and wireless networks. The development of group III-nitride devices is often limited by film cracking which results from intrinsic and extrinsic stress due to lattice and thermal expansion mismatches between the film and substrate. The research is focused on understanding the microstructural mechanisms responsible for film stress and developing strategies to mitigate stress and film cracking. In-situ laser reflectance is used to study dynamic changes in film stress during deposition. This information is correlated to changes in film microstructure and dislocation density measured post-growth and is used to develop models of stress generation and relaxation in the group III-nitride materials system.