Results | SCSU Bibliography

Kornblum, L., Jin, E. N., Kumah, D., Ernst, A. T., Broadbridge, C., Ahn, C. H., & Walker, F. (2015). Oxide 2D electron gases as a route for high carrier densities on (001) Si. Applied Physics Letters, 106(20), 201602. https://doi.org/10.1063/1.4921437

Two dimensional electron gases (2DEGs) formed at the interfaces of oxide heterostructures draw considerable interest owing to their unique physics and potential applications. Growing such heterostructures on conventional semiconductors has the potential to integrate their functionality with semiconductor device technology. We demonstrate 2DEGs on a conventional semiconductor by growing GdTiO3-SrTiO3 on silicon. Structural analysis confirms the epitaxial growth of heterostructures with abrupt interfaces and a high degree of crystallinity. Transport measurements show the conduction to be an interface effect, ∼9 × 1013 cm-2 electrons per interface. Good agreement is demonstrated between the electronic behavior of structures grown on Si and on an oxide substrate, validating the robustness of this approach to bridge between lab-scale samples to a scalable, technologically relevant materials system. © 2015 AIP Publishing LLC.

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Jin, E. N., Kornblum, L., Kumah, D., Zou, K., Broadbridge, C., Ngai, J. H., Ahn, C. H., & Walker, F. (2014). A high density two-dimensional electron gas in an oxide heterostructure on Si (001). APL Materials, 2(11), 116109. https://doi.org/10.1063/1.4902433

We present the growth and characterization of layered heterostructures comprised of LaTiO3 and SrTiO3 epitaxially grown on Si (001). Magnetotransport measurements show that the sheet carrier densities of the heterostructures scale with the number of LaTiO3/SrTiO3 interfaces, consistent with the presence of an interfacial 2-dimensional electron gas (2DEG) at each interface. Sheet carrier densities of 8.9 × 1014 cm-2 per interface are observed. Integration of such high density oxide 2DEGs on silicon provides a bridge between the exceptional properties and functionalities of oxide 2DEGs and microelectronic technologies. © 2014 Author(s).

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Liu, J., Liu, Y., Gong, P., Li, Y., Moore, K. M., Scanley, E., Walker, F., Broadbridge, C., & Schroers, J. (2015). Combinatorial exploration of color in gold-based alloys. Gold Bulletin, 48(3–4), 111–118. https://doi.org/10.1007/s13404-015-0167-z

Combinatorial approaches comprised of combinatorial magnetron co-sputtering deposition and fast screening methods are introduced to study color as a function of composition in Au-based alloys. The microstructures of the thin films and bulk alloys are identified by X-ray diffraction, and their colors of the alloys are characterized by optical reflectivity. The results reveal that when comparing microstructures and reflectivity, thin films are similar to bulk alloys. In Au-Ag-Cu solid solutions, the color of the ternary alloy follows the rule of mixture. For colors resulting from AuAl2 intermetallic, the color of an alloy scales with the percentage of the intermetallic phase and the deviation from its ideal binary composition. In the Au-Al-Cu library, we found a ∼90 % AuAl2 area fraction compositional window where copper addition can be tuned to improve mechanical properties while keeping purple color, even though Al and CuAl2 phases exist. Moreover, when comparing the color in Au-Cu-Si-Ag amorphous and crystalline state solid solution for the same composition, the colors are essentially identical. © 2015 The Author(s).

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Su, D., Vaz, C. A. F., Segal, Y., Walker, F., Ahn, C. H., Han, M.-G., Sawicki, M., & Broadbridge, C. (2011). Domain pinning and valence state switching in Pb(Zr0.2Ti0.8)O3/La0.8Sr0.2MnO3 heterostructures. Microscopy and Microanalysis, 17(S2), 1400–1401. https://doi.org/10.1017/s1431927611007872

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Broadbridge, C., Garofano, J., Altman, E. I., Khalil, Y. F., Henrich, V. E., Segal, Y., Padmore, M., Michael, P., & Walker, F. (2009). Research grade instrumentation for nanotechnology and MSE education. MRS Proceedings, 1233, 17–22. https://doi.org/10.1557/PROC-1233-PP10-03

The Center for Research on Interface Structures and Phenomena (CRISP) is a National Science Foundation (NSF) Materials Research Science and Engineering Center (MRSEC). CRISP is a partnership between Yale University, Southern Connecticut State University (SCSU) and Brookhaven National Laboratory. A main focus of CRISP research is complex oxide interfaces that are prepared using epitaxial techniques, including molecular beam epitaxy (MBE). Complex oxides exhibit a wealth of electronic, magnetic and chemical behaviors, and the surfaces and interfaces of complex oxides can have properties that differ substantially from those of the corresponding bulk materials. CRISP employs this research program in a concerted way to educate students at all levels. CRISP has constructed a robust MBE apparatus specifically designed for safe and productive use by undergraduates. Students can grow their own samples and then characterize them with facilities at both Yale and SCSU, providing a complete research and educational experience. This paper will focus on the implementation of the CRISP Teaching MBE facility and its use in the study of the synthesis and properties of the crystalline oxide-silicon interface. C 2010 Materials Research Society.

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Su, D., Yang, B., Jiang, N., Sawicki, M., Broadbridge, C., Couillard, M., Reiner, J. W., Walker, F., Ahn, C. H., & Zhu, Y. (2010). Valence electron energy-loss spectroscopy of ultrathin SrTiO3 films grown on silicon (100) single crystal. Applied Physics Letters, 96(12), 121914. https://doi.org/10.1063/1.3364144

Valence electron energy-loss spectroscopy is used to investigate the plasmon excitations of ultrathin SrTiO3 sandwiched between amorphous Si and crystalline Si. Two plasmon excitations were observed, one at 15.8 eV and the other at 28.7 eV. Our calculations, based on dielectric-function theory, suggest that the former peak originates from the coupling of the Si layers and is related to the geometry of the structure, and the latter peak results from the SrTiO3 bulk plasmon after a redshift. Our findings demonstrate the value of valence electron energy-loss spectroscopy in detecting a local change in the effective electron mass. © 2010 American Institute of Physics.

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Su, D., Meng, Q., Vaz, C. A. F., Han, M.-G., Segal, Y., Walker, F., Sawicki, M., Broadbridge, C., & Ahn, C. H. (2011). Origin of 90° domain wall pinning in Pb(Zr0.2Ti0.8)O3 heteroepitaxial thin films. Applied Physics Letters, 99(10), 102902. https://doi.org/10.1063/1.3634028

We describe a transmission-electron-microscopy study of the ferroelectric domains in an epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) film grown on La0.7Sr0.3MnO3/SrTiO 3(001). We directly observe the pinning of 90 domain walls by pairs of misfit dislocations, respectively, with Burgers vectors a [100] and a [001]. Model calculations based on the elastic theory confirm our finding that, in addition to the depolarization field surrounding the dislocation, the strain field of misfit dislocation-pairs plays the primary role in the formation and pinning of a domains. © 2011 American Institute of Physics.

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Kumah, D., Reiner, J. W., Segal, Y., Kolpak, A. M., Zhang, Z., Su, D., Zhu, Y., Sawicki, M., Broadbridge, C., Ahn, C. H., & Walker, F. (2010). The atomic structure and polarization of strained SrTiO3/Si. Applied Physics Letters, 97(25), 251902. https://doi.org/10.1063/1.3529460

For thin film devices based on coupling ferroelectric polarization to charge carriers in semiconductors, the role of the interface is critical. To elucidate this role, we use synchrotron x-ray diffraction to determine the interface structure of epitaxial SrTiO3 grown on the (001) surface of Si. The average displacement of the O octahedral sublattice relative to the Sr sublattice determines the film polarization and is measured to be about 0.05 nm toward the Si, with Ti off-center displacements 0.009 nm away from the substrate. Measurements of films with different boundary conditions on the top of the SrTiO3 show that the polarization at the SrTiO3 /Si interface is dominated by oxide-Si chemical interactions. © 2010 American Institute of Physics.

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