Maxwell Wetherington
Pennsylvania State University
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Featured researches published by Maxwell Wetherington.
Nano Letters | 2009
Joshua A. Robinson; Maxwell Wetherington; Joseph L. Tedesco; P. M. Campbell; Xiaojun Weng; Joseph Stitt; Mark A. Fanton; Eric Frantz; David W. Snyder; Brenda L. VanMil; Glenn G. Jernigan; Rachael L. Myers-Ward; Charles R. Eddy; D. Kurt Gaskill
We report a direct correlation between carrier mobility and Raman topography of epitaxial graphene (EG) grown on silicon carbide (SiC). We show the Hall mobility of material on SiC(0001) is highly dependent on thickness and monolayer strain uniformity. Additionally, we achieve high mobility epitaxial graphene (18100 cm(2)/(V s) at room temperature) on SiC(0001) and show that carrier mobility depends strongly on the graphene layer stacking.
ACS Nano | 2010
Joshua A. Robinson; Xiaojun Weng; Kathleen A. Trumbull; Randall Cavalero; Maxwell Wetherington; Eric Frantz; Michael LaBella; Zachary Hughes; Mark A. Fanton; David W. Snyder
A promising route for the synthesis of large-area graphene, suitable for standard device fabrication techniques, is the sublimation of silicon from silicon carbide at elevated temperatures (>1200 degrees C). Previous reports suggest that graphene nucleates along the (110n) plane, known as terrace step edges, on the silicon carbide surface. However, to date, a fundamental understanding of the nucleation of graphene on silicon carbide is lacking. We provide the first direct evidence that nucleation of epitaxial graphene on silicon carbide occurs along the (110n) plane and show that the nucleated graphene quality improves as the synthesis temperature is increased. Additionally, we find that graphene on the (110n) plane can be significantly thicker than its (0001) counterpart and appears not to have a thickness limit. Finally, we find that graphene along the (110n) plane can contain a high density of structural defects, often the result of the underlying substrate, which will undoubtedly degrade the electronic properties of the material. Addressing the presence of non-uniform graphene that may contain structural defects at terrace step edges will be key to the development of a large-scale graphene technology derived from silicon carbide.
ACS Nano | 2012
Michael S. Bresnehan; Matthew J. Hollander; Maxwell Wetherington; Michael LaBella; Kathleen A. Trumbull; Randal Cavalero; David W. Snyder; Joshua A. Robinson
Hexagonal boron nitride (h-BN) is a promising dielectric material for graphene-based electronic devices. Here we investigate the potential of h-BN gate dielectrics, grown by chemical vapor deposition (CVD), for integration with quasi-freestanding epitaxial graphene (QFEG). We discuss the large scale growth of h-BN on copper foil via a catalytic thermal CVD process and the subsequent transfer of h-BN to a 75 mm QFEG wafer. X-ray photoelectron spectroscopy (XPS) measurements confirm the absence of h-BN/graphitic domains and indicate that the film is chemically stable throughout the transfer process, while Raman spectroscopy indicates a 42% relaxation of compressive stress following removal of the copper substrate and subsequent transfer of h-BN to QFEG. Despite stress-induced wrinkling observed in the films, Hall effect measurements show little degradation (<10%) in carrier mobility for h-BN coated QFEG. Temperature dependent Hall measurements indicate little contribution from remote surface optical phonon scattering and suggest that, compared to HfO(2) based dielectrics, h-BN can be an excellent material for preserving electrical transport properties. Graphene transistors utilizing h-BN gates exhibit peak intrinsic cutoff frequencies >30 GHz (2.4× that of HfO(2)-based devices).
Applied Physics Letters | 2010
Joseph L. Tedesco; Glenn G. Jernigan; James C. Culbertson; Jennifer K. Hite; Y. Yang; K. M. Daniels; R. L. Myers-Ward; Charles R. Eddy; Joshua A. Robinson; Kathleen A. Trumbull; Maxwell Wetherington; P. M. Campbell; D. K. Gaskill
Epitaxial graphene layers were grown on the C-face of 4H–SiC and 6H–SiC using an argon-mediated growth process. Variations in growth temperature and pressure were found to dramatically affect the morphological properties of the layers. The presence of argon during growth slowed the rate of graphene formation on the C-face and led to the observation of islanding. The similarity in the morphology of the islands and continuous films indicated that island nucleation and coalescence is the growth mechanism for C-face graphene.
Applied Physics Letters | 2011
Joshua A. Robinson; Kathleen A. Trumbull; Michael LaBella; Randall Cavalero; Matthew J. Hollander; Michael Zhu; Maxwell Wetherington; Mark A. Fanton; David W. Snyder
We investigate graphene transport and structural properties as a function of silicon carbide (SiC) wafer orientation. Terrace step edge density is found to increase with wafer misorientation from SiC(0001). This results in a monotonic increase in average graphene thickness, as well as a 30% increase in carrier density and 40% decrease in mobility up to 0.45° miscut toward (11¯00). Beyond 0.45°, average thickness and carrier density continues to increase; however, carrier mobility is similar to low-miscut angles, suggesting that the interaction between graphene and SiC(0001) may be fundamentally different that of graphene/SiC(11¯0n).
Proceedings of SPIE | 2012
Joshua A. Robinson; Maxwell Wetherington; Zachary Hughes; Michael LaBella; Michael S. Bresnehan
Current state-of-the-art nanotechnology offers multiple benefits for radiation sensing applications. These include the ability to incorporate nano-sized radiation indicators into widely used materials such as paint, corrosion-resistant coatings, and ceramics to create nano-composite materials that can be widely used in everyday life. Additionally, nanotechnology may lead to the development of ultra-low power, flexible detection systems that can be embedded in clothing or other systems. Graphene, a single layer of graphite, exhibits exceptional electronic and structural properties, and is being investigated for high-frequency devices and sensors. Previous work indicates that graphene-oxide (GO) - a derivative of graphene - exhibits luminescent properties that can be tailored based on chemistry; however, exploration of graphene-oxides ability to provide a sufficient change in luminescent properties when exposed to gamma or neutron radiation has not been carried out. We investigate the mechanisms of radiation-induced chemical modifications and radiation damage induced shifts in luminescence in graphene-oxide materials to provide a fundamental foundation for further development of radiation sensitive detection architectures. Additionally, we investigate the integration of hexagonal boron nitride (hBN) with graphene-based devices to evaluate radiation induced conductivity in nanoscale devices. Importantly, we demonstrate the sensitivity of graphene transport properties to the presence of alpha particles, and discuss the successful integration of hBN with large area graphene electrodes as a means to provide the foundation for large-area nanoscale radiation sensors.
2D Materials | 2016
Ganesh R. Bhimanapati; Maxwell Wetherington; Shawn Mahabir; Joshua A. Robinson
Since graphene, there has been a focus on several two-dimensional material systems (e.g. boron nitride, borocarbon nitride (BCN), transition-metal dichalcogenides) that provide an even wider array of unique chemistries and properties to explore future applications. Specifically, tailoring graphene/boron nitride heterostructures—which can theoretically retain the character of a single-atom thick sheet, withstand large physical strains, are easily functionalized, and have entirely different optical and mechanical properties compared to graphene—can provide the foundation for entirely new research avenues. In recent years, it has been shown that because of the similar crystal structure, carbon, boron, and nitrogen can co-exist as atomic sheets in a layered structure. We have developed a facile method of integrating boron nitride (hBN) and graphene oxide (GO) via chemical exfoliation which we refer to as BCON. The study of the stability of this material at different pH conditions indicates a stable and a uniform solution is achievable at pH 4–8. X-Ray Photoelectron Spectroscopy helped to identify the new bonds which indicated the formation of BCON linkage. Further, an in situ XPS technique was used to understand the chemical changes while exposing it to ionization radiation specially focusing on the C/O ratio. It was observed that even with a very low energy source, this material is highly sensitive to ionizing radiation, such as neutron, alpha and beta particles.
Journal of Materials Research | 2014
Michael S. Bresnehan; Matthew J. Hollander; Maxwell Wetherington; Ke Wang; Takahira Miyagi; Gregory Pastir; David W. Snyder; Jamie J. Gengler; Andrey A. Voevodin; W. C. Mitchel; Joshua A. Robinson
Bulletin of the American Physical Society | 2017
Megan Farell; Maxwell Wetherington; Joshua A. Robinson; Manish Kumar
arXiv: Materials Science | 2009
Joshua A. Robinson; Kathleen A. Trumbull; Randall Cavalero; Xiaojun Weng; Maxwell Wetherington; Eric Frantz; Michael LaBella; Zachary Hughes; Mark A. Fanton; David W. Snyder