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A wide variety of materials can be isolated into large-area, thin sheets. These new structural elements range from graphene and transition metal dichalcogenides, i.e., true 2D materials, to inorganic nanomembranes (NMs), including single-crystal semiconductor sheets with thickness in the range of 10s-1000s nm. Materials in sheet form provide a platform for fascinating new science and numerous technology breakthroughs. The key enablers of this platform are compliancy/flexibility, ready strain management, a large surface-area-to-volume ratio, and, in semiconductors, the ability to manipulate electronic/optoelectronic properties. In our research group we build on this progress to provide opportunity for new science and for advanced materials that may enable better performance in device structures of dizzying diversity.
The overarching goals of our research program are:
(i) developing novel techniques to isolate an increasingly wide variety of inorganic materials in the form of thin sheets;
(ii) uncovering the impact of thinness, proximity of surfaces and interfaces, and strain fields on the fundamental properties of materials and devices;
(iii) enabling hybrid materials with attributes which are not accessible by single materials.
Check out some of the projects that we are currently working on!
Synthesis and processing of energy-relevant materials based on nanomembranes.
Synthesis and processing of energy-relevant materials based on nanomembranes.
More details coming soon.
Self-assembled slow-wave structures for mm and sub-mm waves.
Self-assembled slow-wave structures for mm and sub-mm waves.
TWTs are vacuum electronic devices that touch our lives every day. They make satellite communications possible because of their exceptional on-orbit reliability and high-power efficiency. TWTs also enable television broadcasting and modern aviation radar systems. No solid-state device can provide as much power as a TWT at wave frequencies. Nevertheless, application of these devices at frequencies beyond the microwaves is limited by a number of challenges that relate to fabricating devices with the required micro- and nanoscale dimensions to amplify THz radiation. We have invented a way to replace the wire helix that is the central feature of a TWT. We are thus able to make micro- and nanoscale diameter structures that are additionally self-winding and mass-producible. We have further developed new ways of testing and qualifying these structures that are potentially more rapid than conventional ones. The upshot is that we can market these helical waveguides to customers who are building high-power, high-frequency amplifiers.
Our approach to miniaturize helical slow-wave structures relies on high-quality nanomembranes or thin slabs of highly conductive materials that spring out of plane and spontaneously form into helices with micro- /nanoscale-diameter and millimeter to centimeter lengths. The target materials are metals and group-IV semiconductors in combination with graphene.
We're testing a new concept to, to build slow-wave structures. Synthesis, assembly, and investigation of structure-property relationships of self-winding helices will be performed for the first time in the context of a vacuum electronic device for amplification of THz waves. The project will coordinate design and modeling, device fabrication, and characterization. The modeling effort will yield an accurate predictive evaluation of proposed designs prior to experimental prototyping and testing. Characterization will range from detailed investigation of the structure of the helices to tests of wave propagation in cold (without e-beam) and hot (with e-beam) helices.
Solid-state THz Sources
Solid-state THz Sources
The overarching goal of this project is to develop a compact THz source which delivers technologically relevant levels of power at room temperature. Our device architecture comprises a monolayer graphene (Gr) formed into a mechanical wiggler on a nano-patterned Ge substrate. Under an applied DC voltage, carriers in the graphene sheet will experience a periodic angular motion and potentially radiate according to a cyclotron-like mechanism.
Bio-device integration
Bio-device integration
The goal of this project is to understand how and to what extent the individual cells alter their structure and their functionality when cultured on unsupported inorganic sheets and on inorganic sheets on highly compliant substrates (i.e., elastomers/hydrogel hybrids). The unique attribute of nanosheets is that their constitutive material provides the electrical and optical functionality necessary to a device operation, while the sheet geometry and the nature of the supporting substrate can be tailored to match the mechanical response of biological tissues. In our group we can tailor and characterize the mechanical response of supported and unsupported nanosheets in a wide range. Additionally, we investigate viability, proliferation, cytoskeleton, and adhesion mechanisms of individual cells on the ultra-thin layers.
Pixelated Photovoltaic Devices
Pixelated Photovoltaic Devices
We harness pixelation of photovoltaic devices to enable integration of thin film solar cells with highly mismatched substrates and devices. By our approach 2D arrays of disorder-free pixels with uniform areas and lateral size of the order of ~0.1-0.5 mm can be consistently transferred to any substrate of choice with a 100% yield.
Solid-phase Epitaxy of Complex Oxide Nanosheets
Solid-phase Epitaxy of Complex Oxide Nanosheets
We investigate crystallization and solid-phase epitaxy of complex oxides under strain and geometrical confinement. The project is a close collaboration with the Wisconsin MRSEC to determine new paradigms for the synthesis of various oxide films including SrTiO3, Al2O3, and PrAl2O3. Our goals are: (i) to provide an improved understanding and predictive capability of the combined effect of strain and geometrical confinement on the density and distribution of structural defects within a crystallized oxide; (ii) to generate new paradigms to integrate single-crystalline oxides and semiconductors.
3D assembly of nanosheets
3D assembly of nanosheets
We establish processes to achieve guided self-assembly of sheets in 3D shapes for a variety of applications ranging from band gap engineering of semicondutors to adavanced neural interfaces
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