Research

Scalable manufacturing of van der Waals (aka, 2D) materials

Naturally-occurring, atomically-thin semiconductors, like molybdenum disulfide, offer a new platform for electronic and optoelectronic devices. They are the semiconducting equivalent of graphene.

Bulk molybdenite––millions of layers of molybdenum disulfide––is abundant, cheap, and high-quality. However, isolating single atomic layers is challenging and time-consuming, and the results are unpredictable, suited only to ad hoc lab-scale devices.

While methods of fabricating these layers from the ground up are maturing, we were interested in devising a way to rapidly and reliably produce single monolayers, in one exfoliation step, in a pattern of our choosing. The patterns we are able to produce are predominantly monolayer material (with aspect ratios of nearly half a million to one). We made a bunch of transistors to demonstrate that the material is undamaged and functions as well as the best lab-grade devices.

H. Gramling, C. M. Towle, S. B. Desai, H. Sun, E. C. Lewis, V. Nguyen, J. W. Ager, D. Chrzan, E. M. Yeatman, A. Javey, H. Taylor, "Repeatable fabrication of patterned monolayer transition metal dichalcogenides with features larger than 10⁴ µm² directly from multilayer sources,” Accepted, ACS Advanced Electronic Materials 2019.
H Gramling, H Taylor, E Yeatman, “Selective Transfer of a Thin Pattern from Layered Material Using a Patterned Handle,” U.S. Provisional Patent No. 62579963.
H Sun, E Sirott, J Mastandrea, H Gramling, et al., “Theory of thin-film-mediated exfoliation of van der Waals bonded layered materials,” Physical Review Materials 2018.

Low-cost nanoscale rheometry

To fabricate nanoscale features, the use of typical micro-patterning approaches involving masked light (photolithography) runs into issues: the scale of the features you want may be smaller than the wavelength of the light you have.

Using physical imprinting, or nanoimprint lithography (NIL), has emerged as a straightforward way of beating the diffraction limit. However, designing process parameters requires an understanding of how the to-be-imprinted material, called resist, behaves under applied pressure from the imprinting stamp. The process of spinning the resist onto a wafer and baking off the solvents changes this behavior appreciably.

We created a system to conduct in situ measurements of these resist films' viscosity, using applied pressure to capture interference patterns and comparing these to the patterns we would predict based on the optical properties of the system.

To allow others to build such a tool in their own labs, we created a system layout plan and viscosity analysis tool for the NanoHUB. We'd like to try using the system to measure the stiffness of other nanoscale things, like cells.

Contact me for a copy of the tool while compatibility issues are being addressed at the NanoHUB.
H. Gramling, Y. Park, H. Taylor (2018), "Nanoscale viscosity extractor," https://nanohub.org/resources/nanovisc.
H. Gramling, H Taylor, “Nanometer-resolution, wide-field optical measurement of time-varying sub-micron fluid film thicknesses for viscosity determination,” Micro-Nano Engineering, Vienna, Austria, 2016 (talk).

Side projects and master's work

Special issue on Scalable Nanomanufacturing, Nature Microsystems & Nanoengineering

E. Yeatman, H. Gramling, E. Wang, "Introduction to the special topic on nanomanufacturing". Microsystems & Nanoengineering 2017. (link)

Chapter, Nanotechnology for consumer electronics, Nanoelectronics

Gramling, H., Kiziroglou, M. and Yeatman, E. Nanotechnology for Consumer Electronics. In: R. Puers, L. Baldi, M. Van de Voorde and S. van Nooten, ed., Nanoelectronics: Materials, Devices, Applications, 1st ed. Wiley-VCH, pp.501-548. (2017). (pdf)

Failure of piezoelectric materials

P Pillatsch, B L Xiao, N Shashoua, H M Gramling, et al., “Degradation of bimorph piezoelectric bending beams in energy harvesting applications,” Smart Materials and Structures 2017. (link)

Failure of biomedical materials

AC Ford, H Gramling, et al., “Micromechanisms of fatigue crack growth in polycarbonate polyurethane: time dependent and hydration effects,” J. Mech. Behavior of Biomedical. Materials. 2018.
N Bonnheim, H Gramling, et al., “Fatigue fracture of a cemented Omnifit™ CoCr femoral stem: implant and failure analysis,” Arthroplasty Today 2017.

Additional first-author conference presentations and talks

1. H. Gramling, E. Yeatman, H. Taylor, “Modeling of van der Waals material delamination,” LRF ICON conference, London, UK, 2018. (talk).
2. H. Gramling, H. Taylor, “Spatially Multiplexed Exfoliation of Single-to- Few-Layer Molybdenum Disulfide,” ASME IMECE 2017, Tampa, Florida, 2017. (talk).
3. H. Gramling, E. Yeatman, H. Taylor, “Interlayer cleavage behavior in van der Waals materials,” 14^th International Conference on Fracture, Rhodes, Greece, 2017 (talk).
4. H. Gramling, E. Yeatman, H. Taylor, “An energetic approach to understanding strain distribution in non-linear layered materials,” LRF ICON conference, Athens, Greece, 2017 (talk).
5. H. Gramling, A. Belinski, J. Sov, T. Norris, S. Gunther, M. Ries, L. Pruitt, “The possibility of cell-induced corrosion of metallic bearing surfaces in total shoulder arthroplasty devices,” 6th International Conference on Mechanics of Biomaterials and Tissues, Waikoloa, Hawaii, 2015 (poster).
6. H. Gramling, N. Bonnheim, M. Ries, S. Shukla, L. Pruitt, “In vivo fracture of a cobalt chromium femoral stem,” 6th International Conference on Mechanics of Biomaterials and Tissues, Waikoloa, Hawaii, 2015 (poster).
7. H. Gramling, A. Srinivasan, L. Pruitt, “Mechanical characterization and a computational wear model for polycarbonate urethane as a bearing material,” Summer Biomechanics, Bioengineering, and Biotransport Conference, Snowbird, Utah, 2015 (poster).
8. H. Gramling, A. Srinivasan, L. Pruitt, “Mechanical and wear characterization of polycarbonate urethane as a viable option for total shoulder replacements,” Orthopedic Research Society Annual Meeting, Las Vegas, Nevada, 2015 (poster).

Google Sites

Report abuse