Clare Boothe Luce Assistant Professor
Dr. Law’s research group in materials science and engineering focuses on the optical properties of novel materials and heterostructures in the mid- and far-infrared. By engineering the material or structure, we can control the way light behaves in these materials, including squeezing light into subwavelength volumes, forcing light to bend backward (negative refraction) or even inducing light to bend around an object in such a way as to render it invisible. The research in this group is focused both on observing and understanding the fundamental optical properties of these structures as well as creating useful devices, such as enhanced infrared detectors, useful for monitoring biological or chemical processes, or superlenses, which allow the viewing structures at length scales below the diffraction limit of light.
- North American Molecular Beam Epitaxy (NAMBE) Young Investigator Award 2016
- Travel grant to attend Texas A&M ADVANCE Workshop 2014
- Travel grant to attend Northeastern ADVANCE Future Faculty Workshop and Materials Genome Initiative Workshop 2013
- Travel grant to attend APS Professional Skills Development Workshop 2012
- Graduate Assistance in Areas of National Need (GAANN) Fellowship 2006-2007
- National Merit Scholar 2002
Molecular beam epitaxy
The Law group uses molecular beam epitaxy (MBE) to grow thin films of interesting materials and heterostructures. MBE is a technique whereby a film is deposited one atomic layer at a time in an ultra high vacuum. This results in crystalline films with few defects and smooth surfaces and also enables abrupt transitions between materials with flat interfaces. We collaborate with the Zide group on the growth of III/V materials and use our own Veeco GenXplor MBE to grow chalcogenide-based topological insulators.
A metamaterial is a material which has structure on a subwavelength scale; one example of this is a layered metallic/dielectric stack in which the layer thickness is much less than the wavelength of light. This subwavelength structure can strongly impact the optical properties of the system, resulting in exotic effects such as a negative index of refraction and leading to devices like superlenses and invisibility cloaks. Most of the research on metamaterials has been performed in the visible frequency range, using traditional metals like gold and silver and traditional dielectrics like silicon dioxide. However, there is significant interest in expanding metamaterial research to the infrared. The infrared wavelength range is home to the fundamental vibrational and rotational resonances of a wide range of molecules and is also the wavelength for thermal emission from most warm objects. Unfortunately, traditional metals and dielectrics can’t be used in the mid-IR, due to their optical properties. Instead, we must look to new materials. Doped semiconductors, in particular, offer a promising alternative. They can be grown by molecular beam epitaxy, so their thicknesses and optical properties can be adjusted as necessary, and they can be integrated with existing optoelectronic devices. The goal of this research project is to investigate layered semiconductor structures for use as mid-IR metamaterials, with the long term goal of creating useful devices such as superlenses.
Topological insulator plasmonics
Topological insulators are a recently-discovered class of materials such as Bi2Se3 and Bi2Te3 which have an insulating bulk, but conducting surfaces on which the electron spin and momentum are locked: an electron with momentum +kx will have spin up (for example), while an electron with momentum -kx will have spin down. These unusual properties are due to the strong spin orbit coupling in these materials, which lead to a band inversion in which the valence band is higher in energy than the conduction band. There is a great deal of interest in the fundamental properties of topological insulators, including the possibility of topological quantum computation. However, we are interested in them for their unique optical properties, specifically, their plasmons.
A plasmon is simply a collective excitation of electrons. The field of plasmonics is concerned with squeezing light into subwavelength volumes. This can strengthen the electric field in and around this volume, resulting in many useful phenomena, such as enhanced sensing of analytes for chemical monitoring of trace gasses or localized heating for photothermal cancer therapy. Topological insulators are predicted to have unique two-dimensional, spin-polarized plasmons. These are interesting for fundamental reasons, as spin-polarized plasmons do not exist in any other system, as well as for applications in spintronics. These plasmonic excitations should have wavelengths in the far-infrared/THz (~2THz). This is a traditionally under-served and difficult wavelength range, though it has significant practical applications such as molecular spectroscopy and imaging. The goal of this project is to investigate the plasmons in topological insulators to first, see if they are indeed spin-polarized and second, to lean how to manipulate them and, eventually, to incorporate topological insulator plasmonic structures into traditional THz devices.
- D. Wei, C. Harris, C. C. Bomberger, J. Zhang, J. Zide, and S. Law. Single-material semiconductor hyperbolic metamaterials. Opt. Exp. 24, 8735-8745 (2016);http://dx.doi.org/10.1364/OE.24.008735
- T. Ginley and S. Law. Growth of Bi2Se3 topological insulator films using a selenium cracker source. J. of Vac. Sci. Technol. B 34, 02L105 (2016);http://dx.doi.org/10.1116/1.4941134
- R. Liu, Y. Zhong, L. Yu, H. Kim, S. Law, J.-M. Zuo, and D. Wasserman. Mid-infrared emission from In(Ga)Sb layers on InAs(Sb). Optics Express 22, 24466 (2014); http://dx.doi.org/10.1364/OE.22.024466
- A. Rosenberg, J. Surya, R. Liu, W. Streyer, S. Law, S. Leslie, R. Bhargava, and D. Wasserman. Flat mid-infrared composite plasmonic materials using lateral doping-patterned semiconductors. Journal of Optics 16, 094012 (2014); http://dx.doi.org/10.1088/2040-8978/16/9/094012
- L. Yu, D. Jung, S. Law, J. Shen, J. J. Cha, M. L. Lee and D. Wasserman. Controlling quantum dot energies using submonolayer bandstructure engineering. Appl. Phys. Lett. 105, 081103 (2014); http://dx.doi.org/10.1063/1.4893983
- S. Law, R. Liu, D. Wasserman. Doped semiconductors with band-edge plasma frequencies. J. Vac. Sci. Technol. B 32, 052601 (2014);http://dx.doi.org/10.1116/1.4891170 Selected as an Editor’s Pick Article!
- W. Streyer, S. Law, A. Rosenberg, C. Roberts, V. A. Podolskiy, A. J. Hoffman, D. Wasserman. Engineering absorption and blackbody radiation in the far-infrared with surface phonon polaritons on gallium phosphide. Appl. Phys. Lett. 104, 131105 (2014); http://dx.doi.org/10.1063/1.4870255
- S. Law, C. Roberts, T. Kilpatrick, L. Yu, T. Ribaudo, E. A. Shaner, V. Podolskiy, D. Wasserman. All-Semiconductor Negative-Index Plasmonic Absorbers. Phys. Rev. Lett. 112, 017401 (2014); http://dx.doi.org/10.1103/PhysRevLett.112.017401
- S. Law, L. Yu, A. Rosenberg, D. Wasserman. All-Semiconductor Plasmonic Nanoantennas for Infrared Sensing. Nano. Lett. 13, 4569 (2013);http://dx.doi.org/10.1021/nl402766t Press: PhysOrg, Nanowerk,
- Y. Zhong, P. B. Dongmo, L. Gong, S. Law, B. Chase, D. Wasserman, J. M. O. Zide. Degenerately doped InGaBiAs:Si as
a highly conductive and transparent contact material in the infrared range. Opt. Mat. Exp. 3, 1197 (2013); http://dx.doi.org/10.1364/OME.3.001197
- J. R. Felts, S. Law, C. M. Roberts, V. Podolskiy, D. M. Wasserman, W. P. King. Near-field infrared absorption of plasmonic semiconductor microparticles studied using atomic force microscope infrared spectroscopy. Appl. Phys. Lett. 102, 152110 (2013); http://dx.doi.org/10.1063/1.4802211 Press:spectroscopynow.com
- W. Streyer, S. Law, G. Rooney, T. Jacobs, D. Wasserman. Strong absorption and selective emission from engineered metals with dielectric coatings. Opt. Exp. 21, 9113 (2013); http://dx.doi.org/10.1364/OE.21.009113
- S. Law, V. Podolskiy, D. Wasserman. Towards nano-scale photonics with micro-scale photons: the opportunities and challenges of mid-infrared plasmonics.Nanophotonics. 2, 103 (2013); http://dx.doi.org/10.1515/nanoph-2012-0027
- S. Law, L. Yu, D. Wasserman. Epitaxial growth of engineered metals for mid-infrared plasmonics.
J. Vac. Sci. Technol. B 31, 03C121 (2013); http://dx.doi.org/10.1116/1.4797487
- L. Yu, S. Law, D. Wasserman. Electroluminescence from quantum dots fabricated with nanosphere lithography. Appl. Phys. Lett. 101, 103105 (2012);http://dx.doi.org/10.1063/1.4751341
- S. Law, D. C. Adams, A. M. Taylor, D. Wasserman. Mid-infrared designer metals. Opt. Exp. 20, 12155 (2012); http://dx.doi.org/10.1364/OE.20.012155
- R. Prozorov, M. D. Vannette, S. A. Law, S. L. Bud’ko and P. C. Canfield. Interplay of local-moment ferromagnetism and superconductivity in ErRh4B4 single crystals. J. Phys.: Conf. Ser. 150 052218 (2009); http://doi:10.1088/1742-6596/150/5/052218
- R. Prozorov, M. D. Vannette, S. A. Law, S. L. Bud’ko, P. C. Canfield. Coexistence of ferromagnetism and superconductivity in ErRh 4 B 4 single crystals probed by dynamic magnetic susceptibility. Phys. Rev. B 77, 100503(R) (2008); http://dx.doi.org/10.1103/PhysRevB.77.100503
- M. D. Vannette, A. S. Sefat, S. Jia, S. A. Law, G. Lapertot, S. L. Bud’ko, P. C. Canfield, J. Schmalian, R. Prozorov. Precise measurements of radio-frequency magnetic susceptibility in ferromagnetic and antiferromagnetic materials. J. Magn. Magn. Mat. 320, 354 (2008); http://dx.doi.org/10.1016/j.jmmm.2007.06.018
- S. L. Bud’ko, S. A. Law, P. C. Canfield, G. D. Samolyuk, M. S. Torikachvili, G. M. Schmiedeshoff. Thermal expansion and magnetostriction of pure and doped RAgSb2 (R= Y, Sm, La) single crystals. J. Phys.: Condens. Matter 20, 115210 (2008); http://dx.doi.org/10.1088/0953-8984/20/11/115210
- M. S. Torikachvili, S. L. Bud’ko, S. A. Law, M. E. Tillman, E. D. Mun, P. C. Canfield. Hydrostatic pressure study of pure and doped La 1− x R x Ag Sb 2 (R= Ce, Nd) charge-density-wave compounds. Phys. Rev. B 76, 235110 (2007); http://dx.doi.org/10.1103/PhysRevB.76.235110
- S. A. Law, S. L. Bud’ko, P. C. Canfield. Effects of mixed rare earth occupancy on the low temperature properties of (R, R′, R ″…) Ni2Ge2 single crystals. J. Magn. Magn. Mat. 312, 140 (2007). http://dx.doi.org/10.1016/j.jmmm.2006.09.028
- R. Prozorov, M. D. Vannette, G. D. Samolyuk, S. A. Law, S. L. Bud’ko, P. C. Canfield. Contactless measurements of Shubnikov-de Haas oscillations in the magnetically ordered state of CeAgSb2 and SmAgSb2 single crystals. Phys. Rev. B 75, 014413 (2007); http://dx.doi.org/10.1103/PhysRevB.75.014413
- J. W. Kim, Y. Lee, D. Wermeille, B. Sieve, L. Tan, S. Law, P. C. Canfield, B. N. Harmon, A. I. Goldman. Systematics of x-ray resonant scattering amplitudes in RNi2Ge2 (R= Gd, Tb, Dy, Ho, Er, Tm): The origin of the branching ratio at the L edges of the heavy rare earths. Phys. Rev. B 72, 064403 (2005); http://dx.doi.org/10.1103/PhysRevB.72.064403